Related
I want to merge several strings in a dataframe based on a groupedby in Pandas.
This is my code so far:
import pandas as pd
from io import StringIO
data = StringIO("""
"name1","hej","2014-11-01"
"name1","du","2014-11-02"
"name1","aj","2014-12-01"
"name1","oj","2014-12-02"
"name2","fin","2014-11-01"
"name2","katt","2014-11-02"
"name2","mycket","2014-12-01"
"name2","lite","2014-12-01"
""")
# load string as stream into dataframe
df = pd.read_csv(data,header=0, names=["name","text","date"],parse_dates=[2])
# add column with month
df["month"] = df["date"].apply(lambda x: x.month)
I want the end result to look like this:
I don't get how I can use groupby and apply some sort of concatenation of the strings in the column "text". Any help appreciated!
You can groupby the 'name' and 'month' columns, then call transform which will return data aligned to the original df and apply a lambda where we join the text entries:
In [119]:
df['text'] = df[['name','text','month']].groupby(['name','month'])['text'].transform(lambda x: ','.join(x))
df[['name','text','month']].drop_duplicates()
Out[119]:
name text month
0 name1 hej,du 11
2 name1 aj,oj 12
4 name2 fin,katt 11
6 name2 mycket,lite 12
I sub the original df by passing a list of the columns of interest df[['name','text','month']] here and then call drop_duplicates
EDIT actually I can just call apply and then reset_index:
In [124]:
df.groupby(['name','month'])['text'].apply(lambda x: ','.join(x)).reset_index()
Out[124]:
name month text
0 name1 11 hej,du
1 name1 12 aj,oj
2 name2 11 fin,katt
3 name2 12 mycket,lite
update
the lambda is unnecessary here:
In[38]:
df.groupby(['name','month'])['text'].apply(','.join).reset_index()
Out[38]:
name month text
0 name1 11 du
1 name1 12 aj,oj
2 name2 11 fin,katt
3 name2 12 mycket,lite
We can groupby the 'name' and 'month' columns, then call agg() functions of Panda’s DataFrame objects.
The aggregation functionality provided by the agg() function allows multiple statistics to be calculated per group in one calculation.
df.groupby(['name', 'month'], as_index = False).agg({'text': ' '.join})
The answer by EdChum provides you with a lot of flexibility but if you just want to concateate strings into a column of list objects you can also:
output_series = df.groupby(['name','month'])['text'].apply(list)
If you want to concatenate your "text" in a list:
df.groupby(['name', 'month'], as_index = False).agg({'text': list})
For me the above solutions were close but added some unwanted /n's and dtype:object, so here's a modified version:
df.groupby(['name', 'month'])['text'].apply(lambda text: ''.join(text.to_string(index=False))).str.replace('(\\n)', '').reset_index()
Please try this line of code : -
df.groupby(['name','month'])['text'].apply(','.join).reset_index()
Although, this is an old question. But just in case. I used the below code and it seems to work like a charm.
text = ''.join(df[df['date'].dt.month==8]['text'])
Thanks to all the other answers, the following is probably the most concise and feels more natural. Using df.groupby("X")["A"].agg() aggregates over one or many selected columns.
df = pandas.DataFrame({'A' : ['a', 'a', 'b', 'c', 'c'],
'B' : ['i', 'j', 'k', 'i', 'j'],
'X' : [1, 2, 2, 1, 3]})
A B X
a i 1
a j 2
b k 2
c i 1
c j 3
df.groupby("X", as_index=False)["A"].agg(' '.join)
X A
1 a c
2 a b
3 c
df.groupby("X", as_index=False)[["A", "B"]].agg(' '.join)
X A B
1 a c i i
2 a b j k
3 c j
I have a dataframe like:
df=pd.DataFrame({
'name1': ['A', 'A', 'C','B','C','A','D'],
'name2': ['D', 'B', 'A','D','B','C','A'],
'text': ['cars', 'cars', 'flower', 'tea','ball','phone','ice'],
'time':['10/01','10/01','10/01','10/01','10/02','10/02','10/02'],
'Flag1':[1,1,2,0,2,1,0],
'Flag2':[0,0,1,0,0,2,1]})
expect:
pd.DataFrame({
'name': ['A', 'B', 'C','D','A','B','C'],
'text': ['cars,flower','cars,tea', 'flower', 'cars,tea','phone,ice','ball','phone'],
'time':['10/01','10/01','10/01','10/01','10/02','10/02','10/02'],
'Flag':[1,0,2,0,1,0,2]})
I want to combine information according to "time". columns are merged by 'time';
'name': 'name1' and 'name2' are merged into 'name';
'words': on each day, words are merged once it shows up in the identical user's row;
'time': the date that the user shows up on that day;
'Flag': 'Flag1' and 'Flag2' are merge into 'Flag'. Each user has a unique
'Flag'('0','1','2') no matter what the date is.
But When I do:
pd.wide_to_long(df, stubnames=["name", "Flag"], i=["text", "time"], j="ref",
suffix="\d*").reset_index().groupby(["name","time"],
as_index=False).agg({"text": ",".join, "Flag": "first"}).sort_values(["time", "name"])
I get:
id variables need to uniquely identify each row
How to deal with that?
Let me know if this works for you. Try :
Reshape by getting the index in, to serve as unique identifier i :
m = pd.wide_to_long(df.reset_index(), stubnames=["name", "Flag"], i="index", j="num")
Munge to get desired output, using groupby and some text manipulation :
(
m.groupby(["name", "time"])
.agg(Flag=("Flag", "first"), text=("text", lambda x: ",".join(set(x))))
.reset_index()
.sort_values("time")
)
name time Flag text
0 A 10/01 1 flower,cars
2 B 10/01 0 tea,cars
4 C 10/01 2 flower
6 D 10/01 0 tea,cars
1 A 10/02 1 phone,ice
3 B 10/02 0 ball
5 C 10/02 2 phone,ball
7 D 10/02 0 ice
I want to change the column labels of a Pandas DataFrame from
['$a', '$b', '$c', '$d', '$e']
to
['a', 'b', 'c', 'd', 'e']
Rename Specific Columns
Use the df.rename() function and refer the columns to be renamed. Not all the columns have to be renamed:
df = df.rename(columns={'oldName1': 'newName1', 'oldName2': 'newName2'})
# Or rename the existing DataFrame (rather than creating a copy)
df.rename(columns={'oldName1': 'newName1', 'oldName2': 'newName2'}, inplace=True)
Minimal Code Example
df = pd.DataFrame('x', index=range(3), columns=list('abcde'))
df
a b c d e
0 x x x x x
1 x x x x x
2 x x x x x
The following methods all work and produce the same output:
df2 = df.rename({'a': 'X', 'b': 'Y'}, axis=1) # new method
df2 = df.rename({'a': 'X', 'b': 'Y'}, axis='columns')
df2 = df.rename(columns={'a': 'X', 'b': 'Y'}) # old method
df2
X Y c d e
0 x x x x x
1 x x x x x
2 x x x x x
Remember to assign the result back, as the modification is not-inplace. Alternatively, specify inplace=True:
df.rename({'a': 'X', 'b': 'Y'}, axis=1, inplace=True)
df
X Y c d e
0 x x x x x
1 x x x x x
2 x x x x x
From v0.25, you can also specify errors='raise' to raise errors if an invalid column-to-rename is specified. See v0.25 rename() docs.
Reassign Column Headers
Use df.set_axis() with axis=1 and inplace=False (to return a copy).
df2 = df.set_axis(['V', 'W', 'X', 'Y', 'Z'], axis=1, inplace=False)
df2
V W X Y Z
0 x x x x x
1 x x x x x
2 x x x x x
This returns a copy, but you can modify the DataFrame in-place by setting inplace=True (this is the default behaviour for versions <=0.24 but is likely to change in the future).
You can also assign headers directly:
df.columns = ['V', 'W', 'X', 'Y', 'Z']
df
V W X Y Z
0 x x x x x
1 x x x x x
2 x x x x x
Just assign it to the .columns attribute:
>>> df = pd.DataFrame({'$a':[1,2], '$b': [10,20]})
>>> df
$a $b
0 1 10
1 2 20
>>> df.columns = ['a', 'b']
>>> df
a b
0 1 10
1 2 20
The rename method can take a function, for example:
In [11]: df.columns
Out[11]: Index([u'$a', u'$b', u'$c', u'$d', u'$e'], dtype=object)
In [12]: df.rename(columns=lambda x: x[1:], inplace=True)
In [13]: df.columns
Out[13]: Index([u'a', u'b', u'c', u'd', u'e'], dtype=object)
As documented in Working with text data:
df.columns = df.columns.str.replace('$', '')
Pandas 0.21+ Answer
There have been some significant updates to column renaming in version 0.21.
The rename method has added the axis parameter which may be set to columns or 1. This update makes this method match the rest of the pandas API. It still has the index and columns parameters but you are no longer forced to use them.
The set_axis method with the inplace set to False enables you to rename all the index or column labels with a list.
Examples for Pandas 0.21+
Construct sample DataFrame:
df = pd.DataFrame({'$a':[1,2], '$b': [3,4],
'$c':[5,6], '$d':[7,8],
'$e':[9,10]})
$a $b $c $d $e
0 1 3 5 7 9
1 2 4 6 8 10
Using rename with axis='columns' or axis=1
df.rename({'$a':'a', '$b':'b', '$c':'c', '$d':'d', '$e':'e'}, axis='columns')
or
df.rename({'$a':'a', '$b':'b', '$c':'c', '$d':'d', '$e':'e'}, axis=1)
Both result in the following:
a b c d e
0 1 3 5 7 9
1 2 4 6 8 10
It is still possible to use the old method signature:
df.rename(columns={'$a':'a', '$b':'b', '$c':'c', '$d':'d', '$e':'e'})
The rename function also accepts functions that will be applied to each column name.
df.rename(lambda x: x[1:], axis='columns')
or
df.rename(lambda x: x[1:], axis=1)
Using set_axis with a list and inplace=False
You can supply a list to the set_axis method that is equal in length to the number of columns (or index). Currently, inplace defaults to True, but inplace will be defaulted to False in future releases.
df.set_axis(['a', 'b', 'c', 'd', 'e'], axis='columns', inplace=False)
or
df.set_axis(['a', 'b', 'c', 'd', 'e'], axis=1, inplace=False)
Why not use df.columns = ['a', 'b', 'c', 'd', 'e']?
There is nothing wrong with assigning columns directly like this. It is a perfectly good solution.
The advantage of using set_axis is that it can be used as part of a method chain and that it returns a new copy of the DataFrame. Without it, you would have to store your intermediate steps of the chain to another variable before reassigning the columns.
# new for pandas 0.21+
df.some_method1()
.some_method2()
.set_axis()
.some_method3()
# old way
df1 = df.some_method1()
.some_method2()
df1.columns = columns
df1.some_method3()
Since you only want to remove the $ sign in all column names, you could just do:
df = df.rename(columns=lambda x: x.replace('$', ''))
OR
df.rename(columns=lambda x: x.replace('$', ''), inplace=True)
Renaming columns in Pandas is an easy task.
df.rename(columns={'$a': 'a', '$b': 'b', '$c': 'c', '$d': 'd', '$e': 'e'}, inplace=True)
df.columns = ['a', 'b', 'c', 'd', 'e']
It will replace the existing names with the names you provide, in the order you provide.
Use:
old_names = ['$a', '$b', '$c', '$d', '$e']
new_names = ['a', 'b', 'c', 'd', 'e']
df.rename(columns=dict(zip(old_names, new_names)), inplace=True)
This way you can manually edit the new_names as you wish. It works great when you need to rename only a few columns to correct misspellings, accents, remove special characters, etc.
One line or Pipeline solutions
I'll focus on two things:
OP clearly states
I have the edited column names stored it in a list, but I don't know how to replace the column names.
I do not want to solve the problem of how to replace '$' or strip the first character off of each column header. OP has already done this step. Instead I want to focus on replacing the existing columns object with a new one given a list of replacement column names.
df.columns = new where new is the list of new columns names is as simple as it gets. The drawback of this approach is that it requires editing the existing dataframe's columns attribute and it isn't done inline. I'll show a few ways to perform this via pipelining without editing the existing dataframe.
Setup 1
To focus on the need to rename of replace column names with a pre-existing list, I'll create a new sample dataframe df with initial column names and unrelated new column names.
df = pd.DataFrame({'Jack': [1, 2], 'Mahesh': [3, 4], 'Xin': [5, 6]})
new = ['x098', 'y765', 'z432']
df
Jack Mahesh Xin
0 1 3 5
1 2 4 6
Solution 1
pd.DataFrame.rename
It has been said already that if you had a dictionary mapping the old column names to new column names, you could use pd.DataFrame.rename.
d = {'Jack': 'x098', 'Mahesh': 'y765', 'Xin': 'z432'}
df.rename(columns=d)
x098 y765 z432
0 1 3 5
1 2 4 6
However, you can easily create that dictionary and include it in the call to rename. The following takes advantage of the fact that when iterating over df, we iterate over each column name.
# Given just a list of new column names
df.rename(columns=dict(zip(df, new)))
x098 y765 z432
0 1 3 5
1 2 4 6
This works great if your original column names are unique. But if they are not, then this breaks down.
Setup 2
Non-unique columns
df = pd.DataFrame(
[[1, 3, 5], [2, 4, 6]],
columns=['Mahesh', 'Mahesh', 'Xin']
)
new = ['x098', 'y765', 'z432']
df
Mahesh Mahesh Xin
0 1 3 5
1 2 4 6
Solution 2
pd.concat using the keys argument
First, notice what happens when we attempt to use solution 1:
df.rename(columns=dict(zip(df, new)))
y765 y765 z432
0 1 3 5
1 2 4 6
We didn't map the new list as the column names. We ended up repeating y765. Instead, we can use the keys argument of the pd.concat function while iterating through the columns of df.
pd.concat([c for _, c in df.items()], axis=1, keys=new)
x098 y765 z432
0 1 3 5
1 2 4 6
Solution 3
Reconstruct. This should only be used if you have a single dtype for all columns. Otherwise, you'll end up with dtype object for all columns and converting them back requires more dictionary work.
Single dtype
pd.DataFrame(df.values, df.index, new)
x098 y765 z432
0 1 3 5
1 2 4 6
Mixed dtype
pd.DataFrame(df.values, df.index, new).astype(dict(zip(new, df.dtypes)))
x098 y765 z432
0 1 3 5
1 2 4 6
Solution 4
This is a gimmicky trick with transpose and set_index. pd.DataFrame.set_index allows us to set an index inline, but there is no corresponding set_columns. So we can transpose, then set_index, and transpose back. However, the same single dtype versus mixed dtype caveat from solution 3 applies here.
Single dtype
df.T.set_index(np.asarray(new)).T
x098 y765 z432
0 1 3 5
1 2 4 6
Mixed dtype
df.T.set_index(np.asarray(new)).T.astype(dict(zip(new, df.dtypes)))
x098 y765 z432
0 1 3 5
1 2 4 6
Solution 5
Use a lambda in pd.DataFrame.rename that cycles through each element of new.
In this solution, we pass a lambda that takes x but then ignores it. It also takes a y but doesn't expect it. Instead, an iterator is given as a default value and I can then use that to cycle through one at a time without regard to what the value of x is.
df.rename(columns=lambda x, y=iter(new): next(y))
x098 y765 z432
0 1 3 5
1 2 4 6
And as pointed out to me by the folks in sopython chat, if I add a * in between x and y, I can protect my y variable. Though, in this context I don't believe it needs protecting. It is still worth mentioning.
df.rename(columns=lambda x, *, y=iter(new): next(y))
x098 y765 z432
0 1 3 5
1 2 4 6
Column names vs Names of Series
I would like to explain a bit what happens behind the scenes.
Dataframes are a set of Series.
Series in turn are an extension of a numpy.array.
numpy.arrays have a property .name.
This is the name of the series. It is seldom that Pandas respects this attribute, but it lingers in places and can be used to hack some Pandas behaviors.
Naming the list of columns
A lot of answers here talks about the df.columns attribute being a list when in fact it is a Series. This means it has a .name attribute.
This is what happens if you decide to fill in the name of the columns Series:
df.columns = ['column_one', 'column_two']
df.columns.names = ['name of the list of columns']
df.index.names = ['name of the index']
name of the list of columns column_one column_two
name of the index
0 4 1
1 5 2
2 6 3
Note that the name of the index always comes one column lower.
Artefacts that linger
The .name attribute lingers on sometimes. If you set df.columns = ['one', 'two'] then the df.one.name will be 'one'.
If you set df.one.name = 'three' then df.columns will still give you ['one', 'two'], and df.one.name will give you 'three'.
BUT
pd.DataFrame(df.one) will return
three
0 1
1 2
2 3
Because Pandas reuses the .name of the already defined Series.
Multi-level column names
Pandas has ways of doing multi-layered column names. There is not so much magic involved, but I wanted to cover this in my answer too since I don't see anyone picking up on this here.
|one |
|one |two |
0 | 4 | 1 |
1 | 5 | 2 |
2 | 6 | 3 |
This is easily achievable by setting columns to lists, like this:
df.columns = [['one', 'one'], ['one', 'two']]
Many of pandas functions have an inplace parameter. When setting it True, the transformation applies directly to the dataframe that you are calling it on. For example:
df = pd.DataFrame({'$a':[1,2], '$b': [3,4]})
df.rename(columns={'$a': 'a'}, inplace=True)
df.columns
>>> Index(['a', '$b'], dtype='object')
Alternatively, there are cases where you want to preserve the original dataframe. I have often seen people fall into this case if creating the dataframe is an expensive task. For example, if creating the dataframe required querying a snowflake database. In this case, just make sure the the inplace parameter is set to False.
df = pd.DataFrame({'$a':[1,2], '$b': [3,4]})
df2 = df.rename(columns={'$a': 'a'}, inplace=False)
df.columns
>>> Index(['$a', '$b'], dtype='object')
df2.columns
>>> Index(['a', '$b'], dtype='object')
If these types of transformations are something that you do often, you could also look into a number of different pandas GUI tools. I'm the creator of one called Mito. It’s a spreadsheet that automatically converts your edits to python code.
Let's understand renaming by a small example...
Renaming columns using mapping:
df = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]}) # Creating a df with column name A and B
df.rename({"A": "new_a", "B": "new_b"}, axis='columns', inplace =True) # Renaming column A with 'new_a' and B with 'new_b'
Output:
new_a new_b
0 1 4
1 2 5
2 3 6
Renaming index/Row_Name using mapping:
df.rename({0: "x", 1: "y", 2: "z"}, axis='index', inplace =True) # Row name are getting replaced by 'x', 'y', and 'z'.
Output:
new_a new_b
x 1 4
y 2 5
z 3 6
Suppose your dataset name is df, and df has.
df = ['$a', '$b', '$c', '$d', '$e']`
So, to rename these, we would simply do.
df.columns = ['a','b','c','d','e']
Let's say this is your dataframe.
You can rename the columns using two methods.
Using dataframe.columns=[#list]
df.columns=['a','b','c','d','e']
The limitation of this method is that if one column has to be changed, full column list has to be passed. Also, this method is not applicable on index labels.
For example, if you passed this:
df.columns = ['a','b','c','d']
This will throw an error. Length mismatch: Expected axis has 5 elements, new values have 4 elements.
Another method is the Pandas rename() method which is used to rename any index, column or row
df = df.rename(columns={'$a':'a'})
Similarly, you can change any rows or columns.
If you've got the dataframe, df.columns dumps everything into a list you can manipulate and then reassign into your dataframe as the names of columns...
columns = df.columns
columns = [row.replace("$", "") for row in columns]
df.rename(columns=dict(zip(columns, things)), inplace=True)
df.head() # To validate the output
Best way? I don't know. A way - yes.
A better way of evaluating all the main techniques put forward in the answers to the question is below using cProfile to gage memory and execution time. #kadee, #kaitlyn, and #eumiro had the functions with the fastest execution times - though these functions are so fast we're comparing the rounding of 0.000 and 0.001 seconds for all the answers. Moral: my answer above likely isn't the 'best' way.
import pandas as pd
import cProfile, pstats, re
old_names = ['$a', '$b', '$c', '$d', '$e']
new_names = ['a', 'b', 'c', 'd', 'e']
col_dict = {'$a': 'a', '$b': 'b', '$c': 'c', '$d': 'd', '$e': 'e'}
df = pd.DataFrame({'$a':[1, 2], '$b': [10, 20], '$c': ['bleep', 'blorp'], '$d': [1, 2], '$e': ['texa$', '']})
df.head()
def eumiro(df, nn):
df.columns = nn
# This direct renaming approach is duplicated in methodology in several other answers:
return df
def lexual1(df):
return df.rename(columns=col_dict)
def lexual2(df, col_dict):
return df.rename(columns=col_dict, inplace=True)
def Panda_Master_Hayden(df):
return df.rename(columns=lambda x: x[1:], inplace=True)
def paulo1(df):
return df.rename(columns=lambda x: x.replace('$', ''))
def paulo2(df):
return df.rename(columns=lambda x: x.replace('$', ''), inplace=True)
def migloo(df, on, nn):
return df.rename(columns=dict(zip(on, nn)), inplace=True)
def kadee(df):
return df.columns.str.replace('$', '')
def awo(df):
columns = df.columns
columns = [row.replace("$", "") for row in columns]
return df.rename(columns=dict(zip(columns, '')), inplace=True)
def kaitlyn(df):
df.columns = [col.strip('$') for col in df.columns]
return df
print 'eumiro'
cProfile.run('eumiro(df, new_names)')
print 'lexual1'
cProfile.run('lexual1(df)')
print 'lexual2'
cProfile.run('lexual2(df, col_dict)')
print 'andy hayden'
cProfile.run('Panda_Master_Hayden(df)')
print 'paulo1'
cProfile.run('paulo1(df)')
print 'paulo2'
cProfile.run('paulo2(df)')
print 'migloo'
cProfile.run('migloo(df, old_names, new_names)')
print 'kadee'
cProfile.run('kadee(df)')
print 'awo'
cProfile.run('awo(df)')
print 'kaitlyn'
cProfile.run('kaitlyn(df)')
df = pd.DataFrame({'$a': [1], '$b': [1], '$c': [1], '$d': [1], '$e': [1]})
If your new list of columns is in the same order as the existing columns, the assignment is simple:
new_cols = ['a', 'b', 'c', 'd', 'e']
df.columns = new_cols
>>> df
a b c d e
0 1 1 1 1 1
If you had a dictionary keyed on old column names to new column names, you could do the following:
d = {'$a': 'a', '$b': 'b', '$c': 'c', '$d': 'd', '$e': 'e'}
df.columns = df.columns.map(lambda col: d[col]) # Or `.map(d.get)` as pointed out by #PiRSquared.
>>> df
a b c d e
0 1 1 1 1 1
If you don't have a list or dictionary mapping, you could strip the leading $ symbol via a list comprehension:
df.columns = [col[1:] if col[0] == '$' else col for col in df]
df.rename(index=str, columns={'A':'a', 'B':'b'})
pandas.DataFrame.rename
If you already have a list for the new column names, you can try this:
new_cols = ['a', 'b', 'c', 'd', 'e']
new_names_map = {df.columns[i]:new_cols[i] for i in range(len(new_cols))}
df.rename(new_names_map, axis=1, inplace=True)
Another way we could replace the original column labels is by stripping the unwanted characters (here '$') from the original column labels.
This could have been done by running a for loop over df.columns and appending the stripped columns to df.columns.
Instead, we can do this neatly in a single statement by using list comprehension like below:
df.columns = [col.strip('$') for col in df.columns]
(strip method in Python strips the given character from beginning and end of the string.)
It is real simple. Just use:
df.columns = ['Name1', 'Name2', 'Name3'...]
And it will assign the column names by the order you put them in.
# This way it will work
import pandas as pd
# Define a dictionary
rankings = {'test': ['a'],
'odi': ['E'],
't20': ['P']}
# Convert the dictionary into DataFrame
rankings_pd = pd.DataFrame(rankings)
# Before renaming the columns
print(rankings_pd)
rankings_pd.rename(columns = {'test':'TEST'}, inplace = True)
You could use str.slice for that:
df.columns = df.columns.str.slice(1)
Another option is to rename using a regular expression:
import pandas as pd
import re
df = pd.DataFrame({'$a':[1,2], '$b':[3,4], '$c':[5,6]})
df = df.rename(columns=lambda x: re.sub('\$','',x))
>>> df
a b c
0 1 3 5
1 2 4 6
My method is generic wherein you can add additional delimiters by comma separating delimiters= variable and future-proof it.
Working Code:
import pandas as pd
import re
df = pd.DataFrame({'$a':[1,2], '$b': [3,4],'$c':[5,6], '$d': [7,8], '$e': [9,10]})
delimiters = '$'
matchPattern = '|'.join(map(re.escape, delimiters))
df.columns = [re.split(matchPattern, i)[1] for i in df.columns ]
Output:
>>> df
$a $b $c $d $e
0 1 3 5 7 9
1 2 4 6 8 10
>>> df
a b c d e
0 1 3 5 7 9
1 2 4 6 8 10
Note that the approaches in previous answers do not work for a MultiIndex. For a MultiIndex, you need to do something like the following:
>>> df = pd.DataFrame({('$a','$x'):[1,2], ('$b','$y'): [3,4], ('e','f'):[5,6]})
>>> df
$a $b e
$x $y f
0 1 3 5
1 2 4 6
>>> rename = {('$a','$x'):('a','x'), ('$b','$y'):('b','y')}
>>> df.columns = pandas.MultiIndex.from_tuples([
rename.get(item, item) for item in df.columns.tolist()])
>>> df
a b e
x y f
0 1 3 5
1 2 4 6
If you have to deal with loads of columns named by the providing system out of your control, I came up with the following approach that is a combination of a general approach and specific replacements in one go.
First create a dictionary from the dataframe column names using regular expressions in order to throw away certain appendixes of column names and then add specific replacements to the dictionary to name core columns as expected later in the receiving database.
This is then applied to the dataframe in one go.
dict = dict(zip(df.columns, df.columns.str.replace('(:S$|:C1$|:L$|:D$|\.Serial:L$)', '')))
dict['brand_timeseries:C1'] = 'BTS'
dict['respid:L'] = 'RespID'
dict['country:C1'] = 'CountryID'
dict['pim1:D'] = 'pim_actual'
df.rename(columns=dict, inplace=True)
If you just want to remove the '$' sign then use the below code
df.columns = pd.Series(df.columns.str.replace("$", ""))
In addition to the solution already provided, you can replace all the columns while you are reading the file. We can use names and header=0 to do that.
First, we create a list of the names that we like to use as our column names:
import pandas as pd
ufo_cols = ['city', 'color reported', 'shape reported', 'state', 'time']
ufo.columns = ufo_cols
ufo = pd.read_csv('link to the file you are using', names = ufo_cols, header = 0)
In this case, all the column names will be replaced with the names you have in your list.
Here's a nifty little function I like to use to cut down on typing:
def rename(data, oldnames, newname):
if type(oldnames) == str: # Input can be a string or list of strings
oldnames = [oldnames] # When renaming multiple columns
newname = [newname] # Make sure you pass the corresponding list of new names
i = 0
for name in oldnames:
oldvar = [c for c in data.columns if name in c]
if len(oldvar) == 0:
raise ValueError("Sorry, couldn't find that column in the dataset")
if len(oldvar) > 1: # Doesn't have to be an exact match
print("Found multiple columns that matched " + str(name) + ": ")
for c in oldvar:
print(str(oldvar.index(c)) + ": " + str(c))
ind = input('Please enter the index of the column you would like to rename: ')
oldvar = oldvar[int(ind)]
if len(oldvar) == 1:
oldvar = oldvar[0]
data = data.rename(columns = {oldvar : newname[i]})
i += 1
return data
Here is an example of how it works:
In [2]: df = pd.DataFrame(np.random.randint(0, 10, size=(10, 4)), columns = ['col1', 'col2', 'omg', 'idk'])
# First list = existing variables
# Second list = new names for those variables
In [3]: df = rename(df, ['col', 'omg'],['first', 'ohmy'])
Found multiple columns that matched col:
0: col1
1: col2
Please enter the index of the column you would like to rename: 0
In [4]: df.columns
Out[5]: Index(['first', 'col2', 'ohmy', 'idk'], dtype='object')
I want to change the column labels of a Pandas DataFrame from
['$a', '$b', '$c', '$d', '$e']
to
['a', 'b', 'c', 'd', 'e']
Rename Specific Columns
Use the df.rename() function and refer the columns to be renamed. Not all the columns have to be renamed:
df = df.rename(columns={'oldName1': 'newName1', 'oldName2': 'newName2'})
# Or rename the existing DataFrame (rather than creating a copy)
df.rename(columns={'oldName1': 'newName1', 'oldName2': 'newName2'}, inplace=True)
Minimal Code Example
df = pd.DataFrame('x', index=range(3), columns=list('abcde'))
df
a b c d e
0 x x x x x
1 x x x x x
2 x x x x x
The following methods all work and produce the same output:
df2 = df.rename({'a': 'X', 'b': 'Y'}, axis=1) # new method
df2 = df.rename({'a': 'X', 'b': 'Y'}, axis='columns')
df2 = df.rename(columns={'a': 'X', 'b': 'Y'}) # old method
df2
X Y c d e
0 x x x x x
1 x x x x x
2 x x x x x
Remember to assign the result back, as the modification is not-inplace. Alternatively, specify inplace=True:
df.rename({'a': 'X', 'b': 'Y'}, axis=1, inplace=True)
df
X Y c d e
0 x x x x x
1 x x x x x
2 x x x x x
From v0.25, you can also specify errors='raise' to raise errors if an invalid column-to-rename is specified. See v0.25 rename() docs.
Reassign Column Headers
Use df.set_axis() with axis=1 and inplace=False (to return a copy).
df2 = df.set_axis(['V', 'W', 'X', 'Y', 'Z'], axis=1, inplace=False)
df2
V W X Y Z
0 x x x x x
1 x x x x x
2 x x x x x
This returns a copy, but you can modify the DataFrame in-place by setting inplace=True (this is the default behaviour for versions <=0.24 but is likely to change in the future).
You can also assign headers directly:
df.columns = ['V', 'W', 'X', 'Y', 'Z']
df
V W X Y Z
0 x x x x x
1 x x x x x
2 x x x x x
Just assign it to the .columns attribute:
>>> df = pd.DataFrame({'$a':[1,2], '$b': [10,20]})
>>> df
$a $b
0 1 10
1 2 20
>>> df.columns = ['a', 'b']
>>> df
a b
0 1 10
1 2 20
The rename method can take a function, for example:
In [11]: df.columns
Out[11]: Index([u'$a', u'$b', u'$c', u'$d', u'$e'], dtype=object)
In [12]: df.rename(columns=lambda x: x[1:], inplace=True)
In [13]: df.columns
Out[13]: Index([u'a', u'b', u'c', u'd', u'e'], dtype=object)
As documented in Working with text data:
df.columns = df.columns.str.replace('$', '')
Pandas 0.21+ Answer
There have been some significant updates to column renaming in version 0.21.
The rename method has added the axis parameter which may be set to columns or 1. This update makes this method match the rest of the pandas API. It still has the index and columns parameters but you are no longer forced to use them.
The set_axis method with the inplace set to False enables you to rename all the index or column labels with a list.
Examples for Pandas 0.21+
Construct sample DataFrame:
df = pd.DataFrame({'$a':[1,2], '$b': [3,4],
'$c':[5,6], '$d':[7,8],
'$e':[9,10]})
$a $b $c $d $e
0 1 3 5 7 9
1 2 4 6 8 10
Using rename with axis='columns' or axis=1
df.rename({'$a':'a', '$b':'b', '$c':'c', '$d':'d', '$e':'e'}, axis='columns')
or
df.rename({'$a':'a', '$b':'b', '$c':'c', '$d':'d', '$e':'e'}, axis=1)
Both result in the following:
a b c d e
0 1 3 5 7 9
1 2 4 6 8 10
It is still possible to use the old method signature:
df.rename(columns={'$a':'a', '$b':'b', '$c':'c', '$d':'d', '$e':'e'})
The rename function also accepts functions that will be applied to each column name.
df.rename(lambda x: x[1:], axis='columns')
or
df.rename(lambda x: x[1:], axis=1)
Using set_axis with a list and inplace=False
You can supply a list to the set_axis method that is equal in length to the number of columns (or index). Currently, inplace defaults to True, but inplace will be defaulted to False in future releases.
df.set_axis(['a', 'b', 'c', 'd', 'e'], axis='columns', inplace=False)
or
df.set_axis(['a', 'b', 'c', 'd', 'e'], axis=1, inplace=False)
Why not use df.columns = ['a', 'b', 'c', 'd', 'e']?
There is nothing wrong with assigning columns directly like this. It is a perfectly good solution.
The advantage of using set_axis is that it can be used as part of a method chain and that it returns a new copy of the DataFrame. Without it, you would have to store your intermediate steps of the chain to another variable before reassigning the columns.
# new for pandas 0.21+
df.some_method1()
.some_method2()
.set_axis()
.some_method3()
# old way
df1 = df.some_method1()
.some_method2()
df1.columns = columns
df1.some_method3()
Since you only want to remove the $ sign in all column names, you could just do:
df = df.rename(columns=lambda x: x.replace('$', ''))
OR
df.rename(columns=lambda x: x.replace('$', ''), inplace=True)
Renaming columns in Pandas is an easy task.
df.rename(columns={'$a': 'a', '$b': 'b', '$c': 'c', '$d': 'd', '$e': 'e'}, inplace=True)
df.columns = ['a', 'b', 'c', 'd', 'e']
It will replace the existing names with the names you provide, in the order you provide.
Use:
old_names = ['$a', '$b', '$c', '$d', '$e']
new_names = ['a', 'b', 'c', 'd', 'e']
df.rename(columns=dict(zip(old_names, new_names)), inplace=True)
This way you can manually edit the new_names as you wish. It works great when you need to rename only a few columns to correct misspellings, accents, remove special characters, etc.
One line or Pipeline solutions
I'll focus on two things:
OP clearly states
I have the edited column names stored it in a list, but I don't know how to replace the column names.
I do not want to solve the problem of how to replace '$' or strip the first character off of each column header. OP has already done this step. Instead I want to focus on replacing the existing columns object with a new one given a list of replacement column names.
df.columns = new where new is the list of new columns names is as simple as it gets. The drawback of this approach is that it requires editing the existing dataframe's columns attribute and it isn't done inline. I'll show a few ways to perform this via pipelining without editing the existing dataframe.
Setup 1
To focus on the need to rename of replace column names with a pre-existing list, I'll create a new sample dataframe df with initial column names and unrelated new column names.
df = pd.DataFrame({'Jack': [1, 2], 'Mahesh': [3, 4], 'Xin': [5, 6]})
new = ['x098', 'y765', 'z432']
df
Jack Mahesh Xin
0 1 3 5
1 2 4 6
Solution 1
pd.DataFrame.rename
It has been said already that if you had a dictionary mapping the old column names to new column names, you could use pd.DataFrame.rename.
d = {'Jack': 'x098', 'Mahesh': 'y765', 'Xin': 'z432'}
df.rename(columns=d)
x098 y765 z432
0 1 3 5
1 2 4 6
However, you can easily create that dictionary and include it in the call to rename. The following takes advantage of the fact that when iterating over df, we iterate over each column name.
# Given just a list of new column names
df.rename(columns=dict(zip(df, new)))
x098 y765 z432
0 1 3 5
1 2 4 6
This works great if your original column names are unique. But if they are not, then this breaks down.
Setup 2
Non-unique columns
df = pd.DataFrame(
[[1, 3, 5], [2, 4, 6]],
columns=['Mahesh', 'Mahesh', 'Xin']
)
new = ['x098', 'y765', 'z432']
df
Mahesh Mahesh Xin
0 1 3 5
1 2 4 6
Solution 2
pd.concat using the keys argument
First, notice what happens when we attempt to use solution 1:
df.rename(columns=dict(zip(df, new)))
y765 y765 z432
0 1 3 5
1 2 4 6
We didn't map the new list as the column names. We ended up repeating y765. Instead, we can use the keys argument of the pd.concat function while iterating through the columns of df.
pd.concat([c for _, c in df.items()], axis=1, keys=new)
x098 y765 z432
0 1 3 5
1 2 4 6
Solution 3
Reconstruct. This should only be used if you have a single dtype for all columns. Otherwise, you'll end up with dtype object for all columns and converting them back requires more dictionary work.
Single dtype
pd.DataFrame(df.values, df.index, new)
x098 y765 z432
0 1 3 5
1 2 4 6
Mixed dtype
pd.DataFrame(df.values, df.index, new).astype(dict(zip(new, df.dtypes)))
x098 y765 z432
0 1 3 5
1 2 4 6
Solution 4
This is a gimmicky trick with transpose and set_index. pd.DataFrame.set_index allows us to set an index inline, but there is no corresponding set_columns. So we can transpose, then set_index, and transpose back. However, the same single dtype versus mixed dtype caveat from solution 3 applies here.
Single dtype
df.T.set_index(np.asarray(new)).T
x098 y765 z432
0 1 3 5
1 2 4 6
Mixed dtype
df.T.set_index(np.asarray(new)).T.astype(dict(zip(new, df.dtypes)))
x098 y765 z432
0 1 3 5
1 2 4 6
Solution 5
Use a lambda in pd.DataFrame.rename that cycles through each element of new.
In this solution, we pass a lambda that takes x but then ignores it. It also takes a y but doesn't expect it. Instead, an iterator is given as a default value and I can then use that to cycle through one at a time without regard to what the value of x is.
df.rename(columns=lambda x, y=iter(new): next(y))
x098 y765 z432
0 1 3 5
1 2 4 6
And as pointed out to me by the folks in sopython chat, if I add a * in between x and y, I can protect my y variable. Though, in this context I don't believe it needs protecting. It is still worth mentioning.
df.rename(columns=lambda x, *, y=iter(new): next(y))
x098 y765 z432
0 1 3 5
1 2 4 6
Column names vs Names of Series
I would like to explain a bit what happens behind the scenes.
Dataframes are a set of Series.
Series in turn are an extension of a numpy.array.
numpy.arrays have a property .name.
This is the name of the series. It is seldom that Pandas respects this attribute, but it lingers in places and can be used to hack some Pandas behaviors.
Naming the list of columns
A lot of answers here talks about the df.columns attribute being a list when in fact it is a Series. This means it has a .name attribute.
This is what happens if you decide to fill in the name of the columns Series:
df.columns = ['column_one', 'column_two']
df.columns.names = ['name of the list of columns']
df.index.names = ['name of the index']
name of the list of columns column_one column_two
name of the index
0 4 1
1 5 2
2 6 3
Note that the name of the index always comes one column lower.
Artefacts that linger
The .name attribute lingers on sometimes. If you set df.columns = ['one', 'two'] then the df.one.name will be 'one'.
If you set df.one.name = 'three' then df.columns will still give you ['one', 'two'], and df.one.name will give you 'three'.
BUT
pd.DataFrame(df.one) will return
three
0 1
1 2
2 3
Because Pandas reuses the .name of the already defined Series.
Multi-level column names
Pandas has ways of doing multi-layered column names. There is not so much magic involved, but I wanted to cover this in my answer too since I don't see anyone picking up on this here.
|one |
|one |two |
0 | 4 | 1 |
1 | 5 | 2 |
2 | 6 | 3 |
This is easily achievable by setting columns to lists, like this:
df.columns = [['one', 'one'], ['one', 'two']]
Many of pandas functions have an inplace parameter. When setting it True, the transformation applies directly to the dataframe that you are calling it on. For example:
df = pd.DataFrame({'$a':[1,2], '$b': [3,4]})
df.rename(columns={'$a': 'a'}, inplace=True)
df.columns
>>> Index(['a', '$b'], dtype='object')
Alternatively, there are cases where you want to preserve the original dataframe. I have often seen people fall into this case if creating the dataframe is an expensive task. For example, if creating the dataframe required querying a snowflake database. In this case, just make sure the the inplace parameter is set to False.
df = pd.DataFrame({'$a':[1,2], '$b': [3,4]})
df2 = df.rename(columns={'$a': 'a'}, inplace=False)
df.columns
>>> Index(['$a', '$b'], dtype='object')
df2.columns
>>> Index(['a', '$b'], dtype='object')
If these types of transformations are something that you do often, you could also look into a number of different pandas GUI tools. I'm the creator of one called Mito. It’s a spreadsheet that automatically converts your edits to python code.
Let's understand renaming by a small example...
Renaming columns using mapping:
df = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]}) # Creating a df with column name A and B
df.rename({"A": "new_a", "B": "new_b"}, axis='columns', inplace =True) # Renaming column A with 'new_a' and B with 'new_b'
Output:
new_a new_b
0 1 4
1 2 5
2 3 6
Renaming index/Row_Name using mapping:
df.rename({0: "x", 1: "y", 2: "z"}, axis='index', inplace =True) # Row name are getting replaced by 'x', 'y', and 'z'.
Output:
new_a new_b
x 1 4
y 2 5
z 3 6
Suppose your dataset name is df, and df has.
df = ['$a', '$b', '$c', '$d', '$e']`
So, to rename these, we would simply do.
df.columns = ['a','b','c','d','e']
Let's say this is your dataframe.
You can rename the columns using two methods.
Using dataframe.columns=[#list]
df.columns=['a','b','c','d','e']
The limitation of this method is that if one column has to be changed, full column list has to be passed. Also, this method is not applicable on index labels.
For example, if you passed this:
df.columns = ['a','b','c','d']
This will throw an error. Length mismatch: Expected axis has 5 elements, new values have 4 elements.
Another method is the Pandas rename() method which is used to rename any index, column or row
df = df.rename(columns={'$a':'a'})
Similarly, you can change any rows or columns.
If you've got the dataframe, df.columns dumps everything into a list you can manipulate and then reassign into your dataframe as the names of columns...
columns = df.columns
columns = [row.replace("$", "") for row in columns]
df.rename(columns=dict(zip(columns, things)), inplace=True)
df.head() # To validate the output
Best way? I don't know. A way - yes.
A better way of evaluating all the main techniques put forward in the answers to the question is below using cProfile to gage memory and execution time. #kadee, #kaitlyn, and #eumiro had the functions with the fastest execution times - though these functions are so fast we're comparing the rounding of 0.000 and 0.001 seconds for all the answers. Moral: my answer above likely isn't the 'best' way.
import pandas as pd
import cProfile, pstats, re
old_names = ['$a', '$b', '$c', '$d', '$e']
new_names = ['a', 'b', 'c', 'd', 'e']
col_dict = {'$a': 'a', '$b': 'b', '$c': 'c', '$d': 'd', '$e': 'e'}
df = pd.DataFrame({'$a':[1, 2], '$b': [10, 20], '$c': ['bleep', 'blorp'], '$d': [1, 2], '$e': ['texa$', '']})
df.head()
def eumiro(df, nn):
df.columns = nn
# This direct renaming approach is duplicated in methodology in several other answers:
return df
def lexual1(df):
return df.rename(columns=col_dict)
def lexual2(df, col_dict):
return df.rename(columns=col_dict, inplace=True)
def Panda_Master_Hayden(df):
return df.rename(columns=lambda x: x[1:], inplace=True)
def paulo1(df):
return df.rename(columns=lambda x: x.replace('$', ''))
def paulo2(df):
return df.rename(columns=lambda x: x.replace('$', ''), inplace=True)
def migloo(df, on, nn):
return df.rename(columns=dict(zip(on, nn)), inplace=True)
def kadee(df):
return df.columns.str.replace('$', '')
def awo(df):
columns = df.columns
columns = [row.replace("$", "") for row in columns]
return df.rename(columns=dict(zip(columns, '')), inplace=True)
def kaitlyn(df):
df.columns = [col.strip('$') for col in df.columns]
return df
print 'eumiro'
cProfile.run('eumiro(df, new_names)')
print 'lexual1'
cProfile.run('lexual1(df)')
print 'lexual2'
cProfile.run('lexual2(df, col_dict)')
print 'andy hayden'
cProfile.run('Panda_Master_Hayden(df)')
print 'paulo1'
cProfile.run('paulo1(df)')
print 'paulo2'
cProfile.run('paulo2(df)')
print 'migloo'
cProfile.run('migloo(df, old_names, new_names)')
print 'kadee'
cProfile.run('kadee(df)')
print 'awo'
cProfile.run('awo(df)')
print 'kaitlyn'
cProfile.run('kaitlyn(df)')
df = pd.DataFrame({'$a': [1], '$b': [1], '$c': [1], '$d': [1], '$e': [1]})
If your new list of columns is in the same order as the existing columns, the assignment is simple:
new_cols = ['a', 'b', 'c', 'd', 'e']
df.columns = new_cols
>>> df
a b c d e
0 1 1 1 1 1
If you had a dictionary keyed on old column names to new column names, you could do the following:
d = {'$a': 'a', '$b': 'b', '$c': 'c', '$d': 'd', '$e': 'e'}
df.columns = df.columns.map(lambda col: d[col]) # Or `.map(d.get)` as pointed out by #PiRSquared.
>>> df
a b c d e
0 1 1 1 1 1
If you don't have a list or dictionary mapping, you could strip the leading $ symbol via a list comprehension:
df.columns = [col[1:] if col[0] == '$' else col for col in df]
df.rename(index=str, columns={'A':'a', 'B':'b'})
pandas.DataFrame.rename
If you already have a list for the new column names, you can try this:
new_cols = ['a', 'b', 'c', 'd', 'e']
new_names_map = {df.columns[i]:new_cols[i] for i in range(len(new_cols))}
df.rename(new_names_map, axis=1, inplace=True)
Another way we could replace the original column labels is by stripping the unwanted characters (here '$') from the original column labels.
This could have been done by running a for loop over df.columns and appending the stripped columns to df.columns.
Instead, we can do this neatly in a single statement by using list comprehension like below:
df.columns = [col.strip('$') for col in df.columns]
(strip method in Python strips the given character from beginning and end of the string.)
It is real simple. Just use:
df.columns = ['Name1', 'Name2', 'Name3'...]
And it will assign the column names by the order you put them in.
# This way it will work
import pandas as pd
# Define a dictionary
rankings = {'test': ['a'],
'odi': ['E'],
't20': ['P']}
# Convert the dictionary into DataFrame
rankings_pd = pd.DataFrame(rankings)
# Before renaming the columns
print(rankings_pd)
rankings_pd.rename(columns = {'test':'TEST'}, inplace = True)
You could use str.slice for that:
df.columns = df.columns.str.slice(1)
Another option is to rename using a regular expression:
import pandas as pd
import re
df = pd.DataFrame({'$a':[1,2], '$b':[3,4], '$c':[5,6]})
df = df.rename(columns=lambda x: re.sub('\$','',x))
>>> df
a b c
0 1 3 5
1 2 4 6
My method is generic wherein you can add additional delimiters by comma separating delimiters= variable and future-proof it.
Working Code:
import pandas as pd
import re
df = pd.DataFrame({'$a':[1,2], '$b': [3,4],'$c':[5,6], '$d': [7,8], '$e': [9,10]})
delimiters = '$'
matchPattern = '|'.join(map(re.escape, delimiters))
df.columns = [re.split(matchPattern, i)[1] for i in df.columns ]
Output:
>>> df
$a $b $c $d $e
0 1 3 5 7 9
1 2 4 6 8 10
>>> df
a b c d e
0 1 3 5 7 9
1 2 4 6 8 10
Note that the approaches in previous answers do not work for a MultiIndex. For a MultiIndex, you need to do something like the following:
>>> df = pd.DataFrame({('$a','$x'):[1,2], ('$b','$y'): [3,4], ('e','f'):[5,6]})
>>> df
$a $b e
$x $y f
0 1 3 5
1 2 4 6
>>> rename = {('$a','$x'):('a','x'), ('$b','$y'):('b','y')}
>>> df.columns = pandas.MultiIndex.from_tuples([
rename.get(item, item) for item in df.columns.tolist()])
>>> df
a b e
x y f
0 1 3 5
1 2 4 6
If you have to deal with loads of columns named by the providing system out of your control, I came up with the following approach that is a combination of a general approach and specific replacements in one go.
First create a dictionary from the dataframe column names using regular expressions in order to throw away certain appendixes of column names and then add specific replacements to the dictionary to name core columns as expected later in the receiving database.
This is then applied to the dataframe in one go.
dict = dict(zip(df.columns, df.columns.str.replace('(:S$|:C1$|:L$|:D$|\.Serial:L$)', '')))
dict['brand_timeseries:C1'] = 'BTS'
dict['respid:L'] = 'RespID'
dict['country:C1'] = 'CountryID'
dict['pim1:D'] = 'pim_actual'
df.rename(columns=dict, inplace=True)
If you just want to remove the '$' sign then use the below code
df.columns = pd.Series(df.columns.str.replace("$", ""))
In addition to the solution already provided, you can replace all the columns while you are reading the file. We can use names and header=0 to do that.
First, we create a list of the names that we like to use as our column names:
import pandas as pd
ufo_cols = ['city', 'color reported', 'shape reported', 'state', 'time']
ufo.columns = ufo_cols
ufo = pd.read_csv('link to the file you are using', names = ufo_cols, header = 0)
In this case, all the column names will be replaced with the names you have in your list.
Here's a nifty little function I like to use to cut down on typing:
def rename(data, oldnames, newname):
if type(oldnames) == str: # Input can be a string or list of strings
oldnames = [oldnames] # When renaming multiple columns
newname = [newname] # Make sure you pass the corresponding list of new names
i = 0
for name in oldnames:
oldvar = [c for c in data.columns if name in c]
if len(oldvar) == 0:
raise ValueError("Sorry, couldn't find that column in the dataset")
if len(oldvar) > 1: # Doesn't have to be an exact match
print("Found multiple columns that matched " + str(name) + ": ")
for c in oldvar:
print(str(oldvar.index(c)) + ": " + str(c))
ind = input('Please enter the index of the column you would like to rename: ')
oldvar = oldvar[int(ind)]
if len(oldvar) == 1:
oldvar = oldvar[0]
data = data.rename(columns = {oldvar : newname[i]})
i += 1
return data
Here is an example of how it works:
In [2]: df = pd.DataFrame(np.random.randint(0, 10, size=(10, 4)), columns = ['col1', 'col2', 'omg', 'idk'])
# First list = existing variables
# Second list = new names for those variables
In [3]: df = rename(df, ['col', 'omg'],['first', 'ohmy'])
Found multiple columns that matched col:
0: col1
1: col2
Please enter the index of the column you would like to rename: 0
In [4]: df.columns
Out[5]: Index(['first', 'col2', 'ohmy', 'idk'], dtype='object')
I have a dataframe with certain values and want to exchange values in one row on a condition. If the value is greater than x I want it to change to zero. I tried with .loc but somehow I get a Keyerror everytime I try. Does .loc work to select rows instead of columns? I used it for columns before, but I cant get it to work for rows.
df = pd.DataFrame({'a': np.random.randn(4), 'b': np.random.randn(4), 'c': np.random.randn(4)})
print(df)
df.loc['Total'] = df.sum()
df.loc[(df['Total'] < x), ['Total']] = 0
I also tried using iloc, but get another error. I dont think its a complex problem, but im kind of stuck, so help would be much appreciated!
You can assign values with loc - first set rows for repalce values by string - here Total, because set row label Total and then compare values of this rows selected by loc - It return boolean mask:
np.random.seed(2019)
df = pd.DataFrame({'a': np.random.randn(4), 'b': np.random.randn(4), 'c': np.random.randn(4)})
print(df)
a b c
0 -0.217679 -0.361865 -0.235634
1 0.821455 0.685609 0.953490
2 1.481278 0.573761 -1.689625
3 1.331864 0.287728 -0.344943
df.loc['Total'] = df.sum()
x = 1
df.loc['Total', df.loc['Total'] < x] = 0
print (df)
a b c
0 -0.217679 -0.361865 -0.235634
1 0.821455 0.685609 0.953490
2 1.481278 0.573761 -1.689625
3 1.331864 0.287728 -0.344943
Total 3.416918 1.185233 0.000000
Detail:
print (df.loc['Total'] < x)
a False
b False
c True
Name: Total, dtype: bool