Python Pandas - Rearrange levels in MultiIndex

To rearrange levels in MultiIndex, use the MultiIndex.reorder_levels() method in Pandas. This method allows you to change the order of hierarchical index levels by specifying a new arrangement.

What is MultiIndex?

MultiIndex is a multi-level, or hierarchical, index object for pandas objects that enables multiple levels of indexing on an axis.

Creating a MultiIndex

First, let's create a MultiIndex from arrays ?

import pandas as pd

# Create arrays for different levels
arrays = [[2, 4, 3, 1], ['Peter', 'Chris', 'Andy', 'Jacob'], [50, 30, 40, 70]]

# Create MultiIndex with named levels
multiIndex = pd.MultiIndex.from_arrays(arrays, names=('rank', 'student', 'points'))

print("Original MultiIndex:")
print(multiIndex)

Original MultiIndex:
MultiIndex([(2, 'Peter', 50),
            (4, 'Chris', 30),
            (3,  'Andy', 40),
            (1, 'Jacob', 70)],
           names=['rank', 'student', 'points'])

Viewing MultiIndex Levels

You can examine the individual levels of the MultiIndex ?

import pandas as pd

arrays = [[2, 4, 3, 1], ['Peter', 'Chris', 'Andy', 'Jacob'], [50, 30, 40, 70]]
multiIndex = pd.MultiIndex.from_arrays(arrays, names=('rank', 'student', 'points'))

print("The levels in MultiIndex:")
print(multiIndex.levels)

The levels in MultiIndex:
[[1, 2, 3, 4], ['Andy', 'Chris', 'Jacob', 'Peter'], [30, 40, 50, 70]]

Reordering MultiIndex Levels

Use reorder_levels() with the order parameter to specify the new level arrangement. The order is specified using level indices ?

import pandas as pd

arrays = [[2, 4, 3, 1], ['Peter', 'Chris', 'Andy', 'Jacob'], [50, 30, 40, 70]]
multiIndex = pd.MultiIndex.from_arrays(arrays, names=('rank', 'student', 'points'))

print("Original MultiIndex:")
print(multiIndex)
print("\nReordered MultiIndex (points, rank, student):")
reordered = multiIndex.reorder_levels(order=[2, 0, 1])
print(reordered)

Original MultiIndex:
MultiIndex([(2, 'Peter', 50),
            (4, 'Chris', 30),
            (3,  'Andy', 40),
            (1, 'Jacob', 70)],
           names=['rank', 'student', 'points'])

Reordered MultiIndex (points, rank, student):
MultiIndex([(50, 2, 'Peter'),
            (30, 4, 'Chris'),
            (40, 3, 'Andy'),
            (70, 1, 'Jacob')],
           names=['points', 'rank', 'student'])

Syntax

MultiIndex.reorder_levels(order)

Parameters

Key Points

• Level indices start from 0 (first level is 0, second is 1, etc.)
• The method returns a new MultiIndex with reordered levels
• Level names are preserved and reordered accordingly
• Original MultiIndex remains unchanged

Conclusion

The reorder_levels() method provides a simple way to rearrange MultiIndex levels by specifying the desired order using level indices. This is useful for reorganizing hierarchical data structures in pandas.