Return multiple columns using Pandas apply() method

Objects passed to the pandas.apply() are Series objects whose index is either the DataFrame’s index (axis=0) or the DataFrame’s columns (axis=1). By default (result_type=None), the final return type is inferred from the return type of the applied function. Otherwise, it depends on the result_type argument.

Syntax:

s.apply(func, convert_dtype=True, args=())

Creating Dataframe to return multiple columns using apply() method

Python3

# Importing required Libraries
import pandas
import numpy

# Creating dataframe
dataFrame = pandas.DataFrame
        ([[4, 9], ] * 3, columns =['A', 'B'])
display(dataFrame)

Output:

Below are some programs which depict the use of pandas.DataFrame.apply() 

Example 1:

Using a Numpy universal function (in this case the same as numpy.sqrt()). 

Python3

# Using pandas.DataFrame.apply() on the data frame
print('Returning multiple columns from Pandas apply()')
dataFrame.apply(numpy.sqrt)

Output:

Returning multiple columns from Pandas apply()
    
A   B
0    2.0    3.0
1    2.0    3.0
2    2.0    3.0

Example 2:

Using a reducing function on columns. 

Python3

# Using pandas.DataFrame.apply() on the data frame
print('Returning multiple columns from Pandas apply()')
dataFrame.apply(numpy.sum, axis = 0)

Output:

Returning multiple columns from Pandas apply()
A    12
B    27
dtype: int64 

Example 3:

Using a reducing function on rows. 

Python3

# Using pandas.DataFrame.apply() on the data frame
print('Returning multiple columns from Pandas apply()')
dataFrame.apply(numpy.sum, axis = 1)

Output:

Returning multiple columns from Pandas apply()
0    13
1    13
2    13
dtype: int64 

Example 4:

Returning a list-like will result in a Series using the lambda function. 

Python3

# Using pandas.DataFrame.apply() on the data frame
print('Returning multiple columns from Pandas apply()')
dataFrame.apply(lambda x: [1, 2], axis = 1)

Output:

Returning multiple columns from Pandas apply()
0    [1, 2]
1    [1, 2]
2    [1, 2]
dtype: object 

Example 5:

Passing result_type=’expand’ will expand list-like results to columns of a Dataframe. 

Python3

# Using pandas.DataFrame.apply() on the data frame
print('Returning multiple columns from Pandas apply()')
dataFrame.apply(lambda x: [1, 2], axis = 1, result_type ='expand')

Output:

Returning multiple columns from Pandas apply()
0    1
0    1    2
1    1    2
2    1    2 

Example 6:

Returning a Series inside the function is similar to passing result_type=’expand’. The resulting column names will be the Series index. 

Python3

# Using pandas.DataFrame.apply() on the data frame
print('Returning multiple columns from Pandas apply()')
dataFrame.apply(lambda x: pandas.Series(
    [1, 2], index =['foo', 'bar']), axis = 1)

Output:

Returning multiple columns from Pandas apply()
foo    bar
0    1    2
1    1    2
2    1    2 

Example 7:

Passing result_type=’broadcast’ will ensure the same shape result, whether list-like or scalar is returned by the function, and broadcasted along the axis. The resulting column names will be the originals.

Python3

# Using pandas.DataFrame.apply() on the data frame
print('Returning multiple columns from Pandas apply()')
dataFrame.apply(lambda x: [1, 2], axis = 1, result_type ='broadcast')

Output:

Returning multiple columns from Pandas apply()
A    B
0    1    2
1    1    2
2    1    2