# Find the union of two NumPy arrays

• Last Updated : 05 Sep, 2020

To find union of two 1-dimensional arrays we can use function numpy.union1d() of Python Numpy library. It returns unique, sorted array with values that are in either of the two input arrays.

Syntax:

```numpy.union1d(array1, array2)
```

Note The arrays given in input are flattened if they are not 1-dimensional.

Let’s see examples of how to find union of two arrays.

Example 1:

 `# import libraries``import` `numpy as np`` ` ` ` `arr1 ``=` `np.array([``10``, ``20``, ``30``, ``40``])``print``(``"array1 "``, arr1)`` ` `arr2 ``=` `np.array([``20``, ``40``, ``60``, ``80``])``print``(``"array2 "``, arr2)`` ` `# print union of the two arrays``print``(``"Union of two arrays :"``, np.union1d(arr1, arr2))`

Output:

Example 2:
Let’s see example of finding union of a 2-d and a 1-d array. As discussed earlier, if array passed as arguments to function numpy.union1d is 2-dimensional, then they are flattened to 1-dimension.

 `# import libraries``import` `numpy as np`` ` ` ` `# 2-d array``arr1 ``=` `np.array([[``1``, ``2``, ``3``], [``4``, ``5``, ``6``]])``print``(``"array1 "``)``print``(arr1)`` ` `arr2 ``=` `np.array([``0``, ``5``, ``10``])``print``(``"array2 "``, arr2)`` ` `# print union of 2-d array and 1-d array``print``(``"Union of two arrays"``, np.union1d(arr1, arr2))`

Output:

Example3:
If we want to find union of more than two arrays, then we can find that by using functools.reduce function.

 `# code to find union of more than two arrays``# import libraries``import` `numpy as np``from` `functools ``import` `reduce`` ` ` ` `array ``=` `reduce``(np.union1d, ([``1``, ``2``, ``3``], [``1``, ``3``, ``5``],``                            ``[``2``, ``4``, ``6``], [``0``, ``0``, ``0``]))``print``(``"Union "``, array)`

Output:

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