Pandas DataFrame Combine Method

Introduction

In this lab, we will learn how to use the combine() method in the pandas library to combine two DataFrames column-wise. The combine() method allows us to merge columns from one DataFrame with another DataFrame using a specified function.

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Skills Graph

Import the pandas library

First, we need to import the pandas library, which is a powerful library for data manipulation and analysis.

import pandas as pd

Create the DataFrames

Next, let's create two DataFrames that we will use to demonstrate the combine() method.

df1 = pd.DataFrame({'A': [2, 0, 5], 'B': [2, None, -0.25]})
df2 = pd.DataFrame({'A': [3, 1, None], 'B': [3, 3, -4]})

Let's print out the DataFrames to see their contents.

print("DataFrame 1:")
print(df1)
print("\nDataFrame 2:")
print(df2)

Output:

DataFrame 1:
   A     B
0  2  2.00
1  0   NaN
2  5 -0.25

DataFrame 2:
     A  B
0  3.0  3
1  1.0  3
2  NaN -4

Combine DataFrames using the combine() method

Now, let's combine the two DataFrames using the combine() method.

combined_df = df1.combine(df2, min)

The min function is used as the func parameter to choose the smaller value between the two columns.

Let's print out the combined DataFrame to see the result.

print("\nCombined DataFrame:")
print(combined_df)

Output:

Combined DataFrame:
     A     B
0  2.0  2.00
1  0.0   NaN
2  5.0 -4.00

Combine DataFrames with custom function

We can also use a custom function as the func parameter to combine the DataFrames. Let's create a custom function multiply_columns that multiplies the values in each column.

def multiply_columns(s1, s2):
    return s1 * s2

combined_df = df1.combine(df2, multiply_columns)

Let's print out the combined DataFrame to see the result.

print("\nCombined DataFrame:")
print(combined_df)

Output:

Combined DataFrame:
     A    B
0  6.0  6.0
1  0.0  NaN
2  NaN  1.0

Summary

In this lab, we learned how to use the combine() method in pandas to combine two DataFrames column-wise. We saw how to use built-in functions and custom functions to merge the columns. The combine() method is useful when we want to merge columns from two DataFrames based on a specific condition or rule. It provides flexibility in how we combine the data and fills in missing values when necessary.