Tracking the source of merged rows using the indicator argument in Pandas

Pandas: Custom Function Exercise-12 with Solution

Write a Pandas program to merge with custom indicator to track source.

In this exercise, we have used the indicator argument in pd.merge() to track the source of each row after merging.

Sample Solution :

Code :

import pandas as pd

# Create two sample DataFrames
df1 = pd.DataFrame({
    'ID': [1, 2, 3],
    'Name': ['Selena', 'Annabel', 'Caeso']
})

df2 = pd.DataFrame({
    'ID': [2, 3, 4],
    'Age': [25, 30, 22]
})

# Merge the DataFrames with an indicator
merged_df = pd.merge(df1, df2, on='ID', how='outer', indicator=True)

# Output the result
print(merged_df)

Output:

   ID     Name   Age      _merge
0   1   Selena   NaN   left_only
1   2  Annabel  25.0        both
2   3    Caeso  30.0        both
3   4      NaN  22.0  right_only     

Explanation:

• Created two DataFrames df1 and df2.
• Used pd.merge() with the indicator=True argument to add a column that shows whether the row came from the left DataFrame, the right, or both.
• The result includes an extra _merge column to track the source of each row.

Python-Pandas Code Editor:

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