Counting Occurrences in an ndarray

In numpy, one can encounter the error "numpy.ndarray object has no attribute count" while attempting to use the .count() method to count the occurrence of a specific value in an array.

Using numpy.unique

A solution to this is using numpy.unique(). This function identifies unique values in an array and provides their corresponding counts. For example, to count the number of 0s and 1s in the array y below:

import numpy

y = np.array([0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1])

unique, counts = numpy.unique(y, return_counts=True)

The unique and counts variables will now hold unique values and their counts respectively.

Non-numpy Method

An alternative method that doesn't require numpy is using the collections.Counter class. This class constructs a dictionary that maps elements to their counts. For instance, to count the occurrence of elements in y using Counter:

import collections, numpy

y = np.array([0, 3, 0, 1, 0, 1, 2, 1, 0, 0, 0, 0, 1, 3, 4])

counter = collections.Counter(y)

The counter variable will now provide the counts of each unique element in y.