Python Pandas - Get location for a label or a tuple of labels in a MultiIndex

To get location for a label or a tuple of labels in a MultiIndex, use the MultiIndex.get_loc() method in Pandas. This method returns the location of a label in the MultiIndex, which can be an integer, slice, or boolean array depending on the label's occurrence.

Basic Syntax

MultiIndex.get_loc(key)

Where key can be a single label or a tuple of labels for multi-level indexing.

Creating a MultiIndex

First, let's create a MultiIndex from arrays ?

import pandas as pd

# Create MultiIndex from arrays
multiIndex = pd.MultiIndex.from_arrays([list('pqrrss'), list('stuvwx')])

print("The MultiIndex...")
print(multiIndex)

The MultiIndex...
MultiIndex([('p', 's'),
            ('q', 't'),
            ('r', 'u'),
            ('r', 'v'),
            ('s', 'w'),
            ('s', 'x')],
           )

Getting Location for Single Label

When a label appears multiple times, get_loc() returns a slice object ?

import pandas as pd

multiIndex = pd.MultiIndex.from_arrays([list('pqrrss'), list('stuvwx')])

# Get location for label 's' (appears at indices 4 and 5)
location = multiIndex.get_loc('s')
print("Location for 's':", location)
print("Type:", type(location))

Location for 's': slice(4, 6, None)
Type: <class 'slice'>

Getting Location for Tuple Labels

For exact tuple matches, the method returns the specific integer index ?

import pandas as pd

multiIndex = pd.MultiIndex.from_arrays([list('pqrrss'), list('stuvwx')])

# Get location for specific tuple
location = multiIndex.get_loc(('r', 'u'))
print("Location for ('r', 'u'):", location)

# Another tuple example
location2 = multiIndex.get_loc(('s', 'w'))
print("Location for ('s', 'w'):", location2)

Location for ('r', 'u'): 2
Location for ('s', 'w'): 4

Practical Example with DataFrame

Here's how to use get_loc() with a DataFrame having MultiIndex ?

import pandas as pd

# Create DataFrame with MultiIndex
index = pd.MultiIndex.from_arrays([
    ['A', 'A', 'B', 'B', 'C', 'C'],
    ['X', 'Y', 'X', 'Y', 'X', 'Y']
], names=['Level1', 'Level2'])

df = pd.DataFrame({'Value': [10, 20, 30, 40, 50, 60]}, index=index)
print("DataFrame:")
print(df)

# Get location for level 'B'
location = df.index.get_loc('B')
print("\nLocation for 'B':", location)

# Get location for specific tuple
location_tuple = df.index.get_loc(('B', 'Y'))
print("Location for ('B', 'Y'):", location_tuple)

DataFrame:
              Value
Level1 Level2      
A      X         10
       Y         20
B      X         30
       Y         40
C      X         50
       Y         60

Location for 'B': slice(2, 4, None)
Location for ('B', 'Y'): 3

Return Types

Conclusion

The MultiIndex.get_loc() method efficiently finds locations of labels in hierarchical indices. It returns integers for exact matches and slice objects for multiple occurrences, making it versatile for MultiIndex navigation.