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How to find the Index of value in Numpy Array ?
• Last Updated : 21 Apr, 2021

In this article, we are going to find the index of the elements present in a NumPy array. The where() method is used to specify the index of a particular element specified in the condition.

Syntax:

numpy.where(condition)

Here, condition is the condition specified.

Example 1:

In this program, we are going to create an array with NumPy and display it.

We can create an array with numpy by using the following syntax:

`numpy.array([value1,value2,value3,.....,value n])`

## Python3

 `# import numpy package ` `import` `numpy as np ` ` `  `# create an numpy array with 1  ` `# to 10 elements ` `a ``=` `np.array([``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8``, ``9``, ``10``]) ` ` `  `print``(a) `

Output:

`[ 1  2  3  4  5  6  7  8  9 10]`

Finding the index of 3

## Python3

 `# display index value ` `# of 3 ` `print``(np.where(a ``=``=` `3``)) `

Output:

`(array(, dtype=int64),)`

Finding index value of 9

## Python3

 `# display index value of 9 ` `print``(np.where(a ``=``=` `9``)) `

Output:

`(array(, dtype=int64),)`

We can also get the index of elements based on multiple conditions. Those conditions are specified in the where() function.

Example 2:

Get the index of elements with a value less than 20 and greater than 12

## Python3

 `# Create a numpy array from a list of numbers ` `# from 11 to 20 ` `a ``=` `np.array([``11``, ``12``, ``13``, ``14``, ``15``, ``16``, ``17``, ``15``, ` `                ``11``, ``12``, ``14``, ``15``, ``16``, ``17``, ``18``, ``19``, ``20``]) ` ` `  `# Get the index of elements with value less  ` `# than 20 and greater than 12 ` `print``("The numbers index locations with the index of \ ` `elements with value less than ``20` `and` `greater than ``12` `are ", ` `      ``np.where((a > ``12``) & (a < ``20``))) `

Output:

The numbers index locations with the index of elements with value less than 20 and greater than 12 are  (array([ 2,  3,  4,  5,  6,  7, 10, 11, 12, 13, 14, 15], dtype=int64),)

Get the index of elements with a value less than 20 and greater than 12

## Python3

 `# Create a numpy array from a list of  ` `# numbers from 11 to 20 ` `a ``=` `np.array([``11``, ``12``, ``13``, ``14``, ``15``, ``16``, ``17``, ``15``, ` `              ``11``, ``12``, ``14``, ``15``, ``16``, ``17``, ``18``, ``19``, ``20``]) ` ` `  `# Get the index of elements with value less  ` `# than 20 or greater than 12 ` `print``("The numbers index locations with the index of \ ` `elements with value less than ``20` `or`  `greater than ``12` `are ", ` `      ``np.where((a > ``12``) | (a < ``20``))) `

Output:

The numbers index locations with the index of elements with value less than 20 or  greater than 12 are  (array([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16]),)

Example 3:

Display element index where values less than 20

## Python3

 `# create numpy array elements ` `a ``=` `np.array([``2``, ``3``, ``4``, ``5``, ``6``, ``45``, ``67``, ``34``]) ` ` `  `# display element index where values  ` `# less than 20 ` `print``(``"element index where values less than 20 : "``,  ` `      ``np.where(a < ``20``)) `

Output:

element index where values less than 20 :  (array([0, 1, 2, 3, 4], dtype=int64),)

Example 4:

Display element index where values greater than 20

## Python3

 `# create numpy array elements ` `a ``=` `np.array([``2``, ``3``, ``4``, ``5``, ``6``, ``45``, ``67``, ``34``]) ` ` `  `# display element index where values  ` `# greater than 20 ` `print``(``"element index where values greater than 20 : "``,  ` `      ``np.where(a > ``20``)) `

Output:

element index where values greater than 20 :  (array([5, 6, 7], dtype=int64),)

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