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Pandas: Group by the first column and get second column as lists in rows

Pandas: DataFrame Exercise-55 with Solution

Write a Pandas program to group by the first column and get second column as lists in rows.

Sample Solution :

Python Code :

import pandas as pd
df = pd.DataFrame( {'col1':['C1','C1','C2','C2','C2','C3','C2'], 'col2':[1,2,3,3,4,6,5]})
print("Original DataFrame")
print(df)
df = df.groupby('col1')['col2'].apply(list)
print("\nGroup on the col1:")
print(df)

Sample Output:

Original DataFrame
  col1  col2
0   C1     1
1   C1     2
2   C2     3
3   C2     3
4   C2     4
5   C3     6
6   C2     5

Group on the col1:
col1
C1          [1, 2]
C2    [3, 3, 4, 5]
C3             [6]
Name: col2, dtype: object

Python-Pandas Code Editor:

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Previous: Write a Pandas program to rename a specific column name in a given DataFrame.
Next: Write a Pandas program to get column index from column name of a given DataFrame.

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Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os 
dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os
cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

  • The os and os.path modules.
  • The __file__ constant
  • os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
  • os.path.dirname(path) (returns "the directory name of pathname path")
  • os.getcwd() (returns "a string representing the current working directory")
  • os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m