Pandas: Joining on index

Last update on May 28 2022 13:07:06 (UTC/GMT +8 hours)

Pandas Joining and merging DataFrame: Exercise-13 with Solution

Write a Pandas program to combine the columns of two potentially differently-indexed DataFrames into a single result DataFrame.

Test Data:

data1:
     A   B
K0  A0  B0
K1  A1  B1
K2  A2  B2

data2:
     C   D
K0  C0  D0
K2  C2  D2
K3  C3  D3

Sample Solution:

Python Code :

import pandas as pd
data1 = pd.DataFrame({'A': ['A0', 'A1', 'A2'],
                      'B': ['B0', 'B1', 'B2']},
                     index=['K0', 'K1', 'K2'])

data2 = pd.DataFrame({'C': ['C0', 'C2', 'C3'],
                      'D': ['D0', 'D2', 'D3']},
                     index=['K0', 'K2', 'K3'])
 
print("Original DataFrames:")
print(data1)
print("--------------------")
print(data2)
print("\nMerged Data (Joining on index):")
result = data1.join(data2)
print(result)

Sample Output:

Original DataFrames:
     A   B
K0  A0  B0
K1  A1  B1
K2  A2  B2
--------------------
     C   D
K0  C0  D0
K2  C2  D2
K3  C3  D3

Merged Data (Joining on index):
     A   B    C    D
K0  A0  B0   C0   D0
K1  A1  B1  NaN  NaN
K2  A2  B2   C2   D2

Python Code Editor:

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Previous: Write a Pandas program to create a combination from two dataframes where a column id combination appears more than once in both dataframes.
Next: Write a Pandas program to merge two given dataframes with different columns.

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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