pandas.Index.union

Index.union(self, other, sort=None)

Form the union of two Index objects.

If the Index objects are incompatible, both Index objects will be cast to dtype(‘object’) first.

Changed in version 0.25.0.

Parameters:

other : Index or array-like

sort : bool or None, default None

Whether to sort the resulting Index.

• None : Sort the result, except when
  1. self and other are equal.
  2. self or other has length 0.
  3. Some values in self or other cannot be compared. A RuntimeWarning is issued in this case.
• False : do not sort the result.

New in version 0.24.0.

Changed in version 0.24.1: Changed the default value from True to None (without change in behaviour).

Returns:

union : Index

Examples

Union matching dtypes

>>> idx1 = pd.Index([1, 2, 3, 4])
>>> idx2 = pd.Index([3, 4, 5, 6])
>>> idx1.union(idx2)
Int64Index([1, 2, 3, 4, 5, 6], dtype='int64')

Union mismatched dtypes

>>> idx1 = pd.Index(['a', 'b', 'c', 'd'])
>>> idx2 = pd.Index([1, 2, 3, 4])
>>> idx1.union(idx2)
Index(['a', 'b', 'c', 'd', 1, 2, 3, 4], dtype='object')