How to find the Cross-section of Pandas Data frame?

Sometimes we need to find the cross-section of pandas series or data frame. Here cross-section means getting values at the specified index, values at several indexes, values at several indexes and levels or values at the specified column and axis etc. There is a function known as pandas.DataFrame.xs() which will help in this condition.

pandas.DataFrame.xs() takes a key argument in order to select data at the particular level in MultiIndex and returns cross-section from pandas data frame.

Syntax: DataFrame.xs(key, axis=0, level=None, drop_level=True)

Parameters:
key – Label contained in the index, or partially in a MultiIndex.
axis – Axis to retrieve cross-section on.
level – In case of a key partially contained in a MultiIndex, indicate which levels are used.
drop_level – If False, returns an object with the same levels as self.

Returns:
Cross-section from the original DataFrame

Below is the pandas code which will help in the proper understanding of pandas.DataFrame.xs() function.

Python3

# importing pandas library
import pandas as pd

# Creating a Dictionary
animal_dict = {'num_of_legs': [4, 0, 4, 2, 2, 2],

               'num_of_wings': [0, 0, 0, 2, 2, 2],

               'class': ['Reptiles', 'Reptiles', 'Reptiles',
                         'Birds', 'Birds', 'Birds'],

               'animal': ['Turtle', 'Snake', 'Crocodile',
                          'Parrot', 'Owl', 'Hummingbird'],

               'locomotion': ['swim_walk', 'swim_crawl', 'swim_walk',
                              'flies', 'flies', 'flies']}

# Converting to Data frame and setting index
df = pd.DataFrame(data=animal_dict)
df = df.set_index(['class', 'animal', 'locomotion'])

# Displaying Data frame
df

Output:

Example 1: Getting values at a specific index

Python3

# Using dataframe.xs() function
# to get values of a specific index
df.xs('Reptiles')

Output:

Example 2: Getting values at several indexes

Python3

# Using dataframe.xs() function
# to get values at several indexes
df.xs(('Birds', 'Parrot'))

Output:

Example 3: Getting values at the specified index and level

Python3

# Using dataframe.xs() function
# to get values at specified index
# and level
df.xs('Crocodile', level = 1)

Output:

Example 4: Getting values at several indexes and levels

Python3

# Using dataframe.xs() function
# to get values at several indexes
# and levels
df.xs(('Birds', 'flies'),
      level=[0, 'locomotion'])

Output:

Example 5: Getting values at the specified column and axis

Python3

# Using dataframe.xs() function
# to get values at specified column
# and axis
df.xs('num_of_wings', axis=1)

Output: