Examples of how to find the number of occurrence of a given element in a matrix with numpy in python ?

### Create a random matrix with numpy

Let's create a random matrix of size (4,4) with random integers between 0 and 4:

`import numpy as np`

`A = np.random.randint(0,5,(4,4))`

returns for example

`[[3 0 2 2]`

`[1 3 4 2]`

`[0 0 3 1]`

`[2 3 3 1]]`

### Find the number of occurrences for each item

To find the number of occurrences for each element one solution is to use the numpy function "unique":

`unique, counts = np.unique(A, return_counts=True)`

`for i in range(len(unique)):`

`print(unique[i],counts[i])`

returns

`0 3`

`1 3`

`2 4`

`3 5`

`4 1`

It is then possible to create a dictionary

`dict(zip(unique, counts))`

returns

`{0: 3, 1: 3, 2: 4, 3: 5, 4: 1}`

### Find the number of occurrences for a given element using where

Another solution to find the occurrence number of 3 using where:

`np.where(A==3)[0].shape[0]`

returns

`5`

### Find the number of occurrences for a given element using the collections module

Another example of how to find the number of occurrences of a given element in an array

`import collections`

`collections.Counter(A.ravel())`

returns

`Counter({3: 5, 0: 3, 2: 4, 1: 3, 4: 1})`