How to import Pandas data frames in a loop [duplicate] - pandas

So what I'm trying to do is the following:
I have 300+ CSVs in a certain folder. What I want to do is open each CSV and take only the first row of each.
What I wanted to do was the following:
import os
list_of_csvs = os.listdir() # puts all the names of the csv files into a list.
The above generates a list for me like ['file1.csv','file2.csv','file3.csv'].
This is great and all, but where I get stuck is the next step. I'll demonstrate this using pseudo-code:
import pandas as pd
for index,file in enumerate(list_of_csvs):
df{index} = pd.read_csv(file)
Basically, I want my for loop to iterate over my list_of_csvs object, and read the first item to df1, 2nd to df2, etc. But upon trying to do this I just realized - I have no idea how to change the variable being assigned when doing the assigning via an iteration!!!
That's what prompts my question. I managed to find another way to get my original job done no problemo, but this issue of doing variable assignment over an interation is something I haven't been able to find clear answers on!

If i understand your requirement correctly, we can do this quite simply, lets use Pathlib instead of os which was added in python 3.4+
from pathlib import Path
csvs = Path.cwd().glob('*.csv') # creates a generator expression.
#change Path(your_path) with Path.cwd() if script is in dif location
dfs = {} # lets hold the csv's in this dictionary
for file in csvs:
dfs[file.stem] = pd.read_csv(file,nrows=3) # change nrows [number of rows] to your spec.
#or with a dict comprhension
dfs = {file.stem : pd.read_csv(file) for file in Path('location\of\your\files').glob('*.csv')}
this will return a dictionary of dataframes with the key being the csv file name .stem adds this without the extension name.
much like
{
'csv_1' : dataframe,
'csv_2' : dataframe
}
if you want to concat these then do
df = pd.concat(dfs)
the index will be the csv file name.

Related

Can we pass dataframes between different notebooks in databricks and sequentially run multiple notebooks? [duplicate]

I have a notebook which will process the file and creates a data frame in structured format.
Now I need to import that data frame created in another notebook, but the problem is before running the notebook I need to validate that only for some scenarios I need to run.
Usually to import all data structures, we use %run. But in my case it should be combinations of if clause and then notebook run
if "dataset" in path": %run ntbk_path
its giving an error " path not exist"
if "dataset" in path": dbutils.notebook.run(ntbk_path)
this one I cannot get all the data structures.
Can someone help me to resolve this error?
To implement it correctly you need to understand how things are working:
%run is a separate directive that should be put into the separate notebook cell, you can't mix it with the Python code. Plus, it can't accept the notebook name as variable. What %run is doing - it's evaluating the code from specified notebook in the context of the current Spark session, so everything that is defined in that notebook - variables, functions, etc. is available in the caller notebook.
dbutils.notebook.run is a function that may take a notebook path, plus parameters and execute it as a separate job on the current cluster. Because it's executed as a separate job, then it doesn't share the context with current notebook, and everything that is defined in it won't be available in the caller notebook (you can return a simple string as execution result, but it has a relatively small max length). One of the problems with dbutils.notebook.run is that scheduling of a job takes several seconds, even if the code is very simple.
How you can implement what you need?
if you use dbutils.notebook.run, then in the called notebook you can register a temp view, and caller notebook can read data from it (examples are adopted from this demo)
Called notebook (Code1 - it requires two parameters - name for view name & n - for number of entries to generate):
name = dbutils.widgets.get("name")
n = int(dbutils.widgets.get("n"))
df = spark.range(0, n)
df.createOrReplaceTempView(name)
Caller notebook (let's call it main):
if "dataset" in "path":
view_name = "some_name"
dbutils.notebook.run(ntbk_path, 300, {'name': view_name, 'n': "1000"})
df = spark.sql(f"select * from {view_name}")
... work with data
it's even possible to do something like with %run, but it could require a kind of "magic". The foundation of it is the fact that you can pass arguments to the called notebook by using the $arg_name="value", and you can even refer to the values specified in the widgets. But in any case, the check for value will happen in the called notebook.
The called notebook could look as following:
flag = dbutils.widgets.get("generate_data")
dataframe = None
if flag == "true":
dataframe = ..... create datarame
and the caller notebook could look as following:
------ cell in python
if "dataset" in "path":
gen_data = "true"
else:
gen_data = "false"
dbutils.widgets.text("gen_data", gen_data)
------- cell for %run
%run ./notebook_name $generate_data=$gen_data
------ again in python
dbutils.widgets.remove("gen_data") # remove widget
if dataframe: # dataframe is defined
do something with dataframe

How to filter Socrata API dataset by multiple values for a single field?

I am attempting to create a CSV file using Python by reading from this specific api:
https://dev.socrata.com/foundry/data.cdc.gov/5jp2-pgaw
Where I'm running into trouble is that I would like to specify multiple values of "loc_admin_zip" to search for at once. For example, returning a CSV file where the zip is either "10001" or "10002". However, I can't figure out how to do this, I can only get it to work if "loc_admin_zip" is set to a single value. Any help would be appreciated. My code so far:
import pandas as pd
from sodapy import Socrata
client = Socrata("data.cdc.gov", None)
results = client.get("5jp2-pgaw",loc_admin_zip = 10002)
results_df = pd.DataFrame.from_records(results)
results_df.to_csv('test.csv')

How to retrieve specific csv column data when multiple conditions are given in Python?

Just like in MySQL query where we retrieve columns with conditions using WHERE clause, how can we do the same in Python? That too with a CSV file?
My CSV File contains data with attributes Name, Place and Color
Ruby,NewYork,Green
Casper,Seoul, Blue
Caroline,NewYork,Green
Now user is given choice to provide city and color name for search. If user input: City = NewYork and Color= Green, It should display
Ruby
Caroline.
How should I do it? I wrote a sample code but output is wrong.
import csv
class Test:
def Display(Name,Place,Color):
f = open('sample.csv')
csv_f = csv.reader(f)
for row in csv_f:
if(row[1]==("NewYork") and row[2] ==("Green")):
pass
print(Name)
Name,Place,Color = input("Enter Details: ").split()
Test.Display(Name,Place,Color)
Consider the following test object:
import csv
class Test:
def display(self, name, place, color):
with open('sample.csv') as csv_file:
csv_reader = csv.reader(csv_file, delimiter=',')
for row in csv_reader:
if(row[1]==place and row[2] == color):
print(row[0])
test = Test()
test.display("Name","NewYork","Green")
We have a Class with a member function for displaying the output.
You can first open the csv file and use the csv_file reference to create your reader in scope. Then you search each row's column for the given strings that you passed into the function.
It looks like you got into a bit of trouble trying to diagnose this one and have left test code in there that has been confusing you.

Prepare a csv file for process mining

hope you are doing well !
I was following tutorials for process mining using 'PM4PY', but I found difficulties in the csv file ,
in my csv file I have this columns : 'id', 'status', 'mailID', 'date'.... ('status' is same as 'activity' that contain some specific choises )
my csv file contains a lot of data.
to follow process mining tutorial I must have in my columns something like 'case:concept:name' ... but I don't know how can I make it
In your case, I assume 'id' would be the same as the Case ID in normal process mining terminology. Similarly, 'status' corresponds to Activity ID and 'date' would correspond to the timestamp.
The best option is to first read into a pandas dataframe before feeding into PM4Py.
For a detailed understanding of how to do this, here is an example below. As you have not mentioned all the columns that you have in your csv file, let us assume that currently you only have [ 'id', 'status', 'date' ] as your column list. The following code can be adapted to any number of columns you have (by adding them to the list named cols) :
import pandas as pd
from pm4py.objects.conversion.log import converter as log_converter
path = '' # Enter path to the csv file
data = pd.read_csv(path)
cols = ['case:concept:name','concept:name','time:timestamp']
data.columns = cols
data['time:timestamp'] = pd.to_datetime(data['time:timestamp'])
data['concept:name'] = data['concept:name'].astype(str)
log = log_converter.apply(data, variant=log_converter.Variants.TO_EVENT_LOG)
Here we have changed the column names and their datatypes as required by the PM4Py package. Convert this dataframe into an event log using the log_converter function. Now you can perform your regular process mining tasks on this event log object. For instance, if you wish to create a Directly-Follows Graph from the event log, you can use the following line of code :
from pm4py.algo.discovery.dfg import algorithm as dfg_algorithm
dfg = dfg_algorithm.apply(log)
first you need import your csv file using pandas, then convert to an event log object, finally you can use in pm4py.
reference:
https://pm4py.fit.fraunhofer.de/documentation

Trying to load an hdf5 table with dataframe.to_hdf before I die of old age

This sounds like it should be REALLY easy to answer with Google but I'm finding it impossible to answer the majority of my nontrivial pandas/pytables questions this way. All I'm trying to do is to load about 3 billion records from about 6000 different CSV files into a single table in a single HDF5 file. It's a simple table, 26 fields, mixture of strings, floats and ints. I'm loading the CSVs with df = pandas.read_csv() and appending them to my hdf5 file with df.to_hdf(). I really don't want to use df.to_hdf(data_columns = True) because it looks like that will take about 20 days versus about 4 days for df.to_hdf(data_columns = False). But apparently when you use df.to_hdf(data_columns = False) you end up with some pile of junk that you can't even recover the table structure from (or so it appears to my uneducated eye). Only the columns that were identified in the min_itemsize list (the 4 string columns) are identifiable in the hdf5 table, the rest are being dumped by data type into values_block_0 through values_block_4:
table = h5file.get_node('/tbl_main/table')
print(table.colnames)
['index', 'values_block_0', 'values_block_1', 'values_block_2', 'values_block_3', 'values_block_4', 'str_col1', 'str_col2', 'str_col3', 'str_col4']
And any query like df = pd.DataFrame.from_records(table.read_where(condition)) fails with error "Exception: Data must be 1-dimensional"
So my questions are: (1) Do I really have to use data_columns = True which takes 5x as long? I was expecting to do a fast load and then index just a few columns after loading the table. (2) What exactly is this pile of garbage I get using data_columns = False? Is it good for anything if I need my table back with query-able columns? Is it good for anything at all?
This is how you can create an HDF5 file from CSV data using pytables. You could also use a similar process to create the HDF5 file with h5py.
Use a loop to read the CSV files with np.genfromtxt into a np array.
After reading the first CSV file, write the data with .create_table() method, referencing the np array created in Step 1.
For additional CSV files, write the data with .append() method, referencing the np array created in Step 1
End of loop
Updated on 6/2/2019 to read a date field (mm/dd/YYY) and convert to datetime object. Note changes to genfromtxt() arguments! Data used is added below the updated code.
import numpy as np
import tables as tb
from datetime import datetime
csv_list = ['SO_56387241_1.csv', 'SO_56387241_2.csv' ]
my_dtype= np.dtype([ ('a',int),('b','S20'),('c',float),('d',float),('e','S20') ])
with tb.open_file('SO_56387241.h5', mode='w') as h5f:
for PATH_csv in csv_list:
csv_data = np.genfromtxt(PATH_csv, names=True, dtype=my_dtype, delimiter=',', encoding=None)
# modify date in fifth field 'e'
for row in csv_data :
datetime_object = datetime.strptime(row['my_date'].decode('UTF-8'), '%m/%d/%Y' )
row['my_date'] = datetime_object
if h5f.__contains__('/CSV_Data') :
dset = h5f.root.CSV_Data
dset.append(csv_data)
else:
dset = h5f.create_table('/','CSV_Data', obj=csv_data)
dset.flush()
h5f.close()
Data for testing:
SO_56387241_1.csv:
my_int,my_str,my_float,my_exp,my_date
0,zero,0.0,0.00E+00,01/01/1980
1,one,1.0,1.00E+00,02/01/1981
2,two,2.0,2.00E+00,03/01/1982
3,three,3.0,3.00E+00,04/01/1983
4,four,4.0,4.00E+00,05/01/1984
5,five,5.0,5.00E+00,06/01/1985
6,six,6.0,6.00E+00,07/01/1986
7,seven,7.0,7.00E+00,08/01/1987
8,eight,8.0,8.00E+00,09/01/1988
9,nine,9.0,9.00E+00,10/01/1989
SO_56387241_2.csv:
my_int,my_str,my_float,my_exp,my_date
10,ten,10.0,1.00E+01,01/01/1990
11,eleven,11.0,1.10E+01,02/01/1991
12,twelve,12.0,1.20E+01,03/01/1992
13,thirteen,13.0,1.30E+01,04/01/1993
14,fourteen,14.0,1.40E+01,04/01/1994
15,fifteen,15.0,1.50E+01,06/01/1995
16,sixteen,16.0,1.60E+01,07/01/1996
17,seventeen,17.0,1.70E+01,08/01/1997
18,eighteen,18.0,1.80E+01,09/01/1998
19,nineteen,19.0,1.90E+01,10/01/1999