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Efficiently replace values from a column to another column Pandas DataFrame
(5 answers)
Closed 10 months ago.
I have created a dataframe called df with this code:
import numpy as np
import pandas as pd
# initialize data of lists.
data = {'Feature1':[1,2,-9999999,4,5],
'Age':[20, 21, 19, 18,34,]}
# Create DataFrame
df = pd.DataFrame(data)
print(df)
The dataframe looks like this:
Feature1 Age
0 1 20
1 2 21
2 -9999999 19
3 4 18
4 5 34
Every time there is a value of -9999999 in column Feature1 I need to replace it with the correspondent value from column Age. so, the output dataframe would look this this:
Feature1 Age
0 1 20
1 2 21
2 19 19
3 4 18
4 5 34
Bear in mind that the actual dataframe that I am using has 200K records (the one I have shown above is just an example).
How do I do that in pandas?
You can use np.where or Series.mask
df['Feature1'] = df['Feature1'].mask(df['Feature1'].eq(-9999999), df['Age'])
# or
df['Feature1'] = np.where(df['Feature1'].eq(-9999999), df['Age'], df['Feature1'])
I have a correlation matrix of stock returns in a Pandas DataFrame and I want to extract the top/bottom 10 correlated pairs from the matrix.
Sample DataFrame:
import pandas as pd
import numpy as np
data = np.random.randint(5,30,size=500)
df = pd.DataFrame(data.reshape((50,10)))
corr = df.corr()
This is my function to get the top/bottom 10 correlated pairs by 1) first returning a multi-indexed series (high) for highest correlated pairs, and then 2) unstacking back into a DataFrame (high_df):
def get_rankings(corr_matrix):
#the matrix is symmetric so we need to extract upper triangle matrix without diagonal (k = 1)
ranked_corr = (corr_matrix.where(np.triu(np.ones(corr_matrix.shape), k=1).astype(np.bool))
.stack()
.sort_values(ascending=False))
high = ranked_corr[:10]
high_df = high.unstack().fillna("")
return high_df
get_rankings(corr)
My current DF output looks something like this:
6 4 5 7 8 3 9
3 0.359 0.198
1 0.275
4 0.257
2 0.176 0.154
0 0.153 0.164
5 0.156
But I want it to look this in either 2/3 columns:
ID1 ID2 Corr
0 9 0.304471
2 8 0.271009
2 3 0.147702
7 9 0.146176
0 7 0.144549
7 8 0.111888
4 6 0.098619
1 7 0.092338
1 4 0.09091
3 6 0.079688
It needs to be in a DataFrame so I can pass it to a grid widget, which only accepts DataFrames. Can anyone help me rehash the shape of the unstacked DF?
I have 3 data frame:
df1
id,k,a,b,c
1,2,1,5,1
2,3,0,1,0
3,6,1,1,0
4,1,0,5,0
5,1,1,5,0
df2
name,a,b,c
p,4,6,8
q,1,2,3
df3
type,w_ave,vac,yak
n,3,5,6
v,2,1,4
from the multiplication, using pandas and numpy, I want to the output in df1:
id,k,a,b,c,w_ave,vac,yak
1,2,1,5,1,16,15,18
2,3,0,1,0,0,3,6
3,6,1,1,0,5,4,7
4,1,0,5,0,0,11,14
5,1,1,5,0,13,12,15
the conditions are:
The value of the new column will be =
#its not a code
df1["w_ave"][1] = df3["w_ave"]["v"]+ df1["a"][1]*df2["a"]["q"]+df1["b"][1]*df2["b"]["q"]+df1["c"][1]*df2["c"]["q"]
for output["w_ave"][1]= 2 +(1*1)+(5*2)+(1*3)
df3["w_ave"]["v"]=2
df1["a"][1]=1, df2["a"]["q"]=1 ;
df1["b"][1]=5, df2["b"]["q"]=2 ;
df1["c"][1]=1, df2["c"]["q"]=3 ;
Which means:
- a new column will be added in df1, from the name of the column from df3.
- for each row of the df1, the value of a, b, c will be multiplied with the same-named q value from df2. and summed together with the corresponding value of df3.
-the column name of df1 , matched will column name of df2 will be multiplied. The other not matched column will not be multiplied, like df1[k].
- However, if there is any 0 in df1["a"], the corresponding output will be zero.
I am struggling with this. It was tough to explain also. My attempts are very silly. I know this attempt will not work. However, I have added this:
import pandas as pd, numpy as np
data1 = "Sample_data1.csv"
data2 = "Sample_data2.csv"
data3 = "Sample_data3.csv"
folder = '~Sample_data/'
df1 =pd.read_csv(folder + data1)
df2 =pd.read_csv(folder + data2)
df3 =pd.read_csv(folder + data3)
df1= df2 * df1
Ok, so this will in no way resemble your desired output, but vectorizing the formula you provided:
df2=df2.set_index("name")
df3=df3.set_index("type")
df1["w_ave"] = df3.loc["v", "w_ave"]+ df1["a"].mul(df2.loc["q", "a"])+df1["b"].mul(df2.loc["q", "b"])+df1["c"].mul(df2.loc["q", "c"])
Outputs:
id k a b c w_ave
0 1 2 1 5 1 16
1 2 3 0 1 0 4
2 3 6 1 1 0 5
3 4 1 0 5 0 12
4 5 1 1 5 0 13
I extracted the following data from a dataframe .
https://i.imgur.com/rCLfV83.jpg
The question is, how do I plot a graph, probably a histogram type, where the horizontal axis are the hours as bins [16:00 17:00 18:00 ...24:00] and the bars are the average rainfall during each of those hours.
I just don't know enough pandas yet to get this off the ground so I need some help. Sample data below as requested.
Date Hours `Precip`
1996-07-30 21 1
1996-08-17 16 1
18 1
1996-08-30 16 1
17 1
19 5
22 1
1996-09-30 19 5
20 5
1996-10-06 20 1
21 1
1996-10-19 18 4
1996-10-30 19 1
1996-11-05 20 3
1996-11-16 16 1
19 1
1996-11-17 16 1
1996-11-29 16 1
1996-12-04 16 9
17 27
19 1
1996-12-12 19 1
1996-12-30 19 10
22 1
1997-01-18 20 1
It seems df is a multi-index DataFrame after a groupby.
Transform the index to a DatetimeIndex
date_hour_idx = df.reset_index()[['Date', 'Hours']] \
.apply(lambda x: '{} {}:00'.format(x['Date'], x['Hours']), axis=1)
precip_series = df.reset_index()['Precip']
precip_series.index = pd.to_datetime(date_hour_idx)
Resample to hours using 'H'
# This will show NaN for hours without an entry
resampled_nan = precip_series.resample('H').asfreq()
# This will fill NaN with 0s
resampled_fillna = precip_series.resample('H').asfreq().fillna(0)
If you want this to be the mean per hour, change your groupby(...).sum() to groupby(...).mean()
You can resample to other intervals too -> pandas resample documentation
More about resampling the DatetimeIndex -> https://pandas.pydata.org/pandas-docs/stable/reference/resampling.html
It seems to be easy when you have data.
I generate artificial data by Pandas for this example:
import pandas as pd
import radar
import random
'''>>> date'''
r2 =()
for a in range(1,51):
t= (str(radar.random_datetime(start='1985-05-01', stop='1985-05-04')),)
r2 = r2 + t
r3 =list(r2)
r3.sort()
#print(r3)
'''>>> variable'''
x = [random.randint(0,16) for x in range(50)]
df= pd.DataFrame({'date': r3, 'measurement': x})
print(df)
'''order'''
col1 = df.join(df['date'].str.partition(' ')[[0,2]]).rename({0: 'daty', 2: 'godziny'}, axis=1)
col2 = df['measurement'].rename('pomiary')
p3 = pd.concat([col1, col2], axis=1, sort=False)
p3 = p3.drop(['measurement'], axis=1)
p3 = p3.drop(['date'], axis=1)
Time for sum and plot:
dx = p3.groupby(['daty']).mean()
print(dx)
import matplotlib.pyplot as plt
dx.plot.bar()
plt.show()
Plot of the mean measurements
Let's say I have something like this:
df = pd.DataFrame({'key':[1,2,3], 'type':[[1,3],[1,2,3],[1,2]], 'value':[5,1,8]})
key type value
1 [1, 3] 5
2 [1, 2, 3] 1
3 [1] 8
Where one of the columns contains a list of items.
I would like to create several rows for each row that contains multiple types.
Ontaining this:
key type value
1 1 5
1 3 5
2 1 1
2 2 1
2 3 1
3 1 8
I've been playing with apply with axis=1 but I can't find a way to return more than 1 row per row of the DataFrame.
Extracting all different 'types' and then looping-concatenating seems to be ugly.
any ideas?
Thanks!!!
import itertools
import pandas as pd
import numpy as np
def melt_series(s):
lengths = s.str.len().values
flat = [i for i in itertools.chain.from_iterable(s.values.tolist())]
idx = np.repeat(s.index.values, lengths)
return pd.Series(flat, idx, name=s.name)
melt_series(df.type).to_frame().join(df.drop('type', 1)).reindex_axis(df.columns, 1)
setup
df = pd.DataFrame({'key':[1,2,3],
'type':[[1,3],[1,2,3],[1,2]],
'value':[5,1,8]})
df