How to Count Occurrences of Elements in a NumPy Array?

Counting Occurrences of Items in an ndarray

To count the occurrence of specific values within a NumPy array, various methods are available.

Using the numpy.unique function:

<code class="python">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)

print(dict(zip(unique, counts)))</code>

This approach generates a dictionary with unique values as keys and their corresponding counts as values. In the example above, it would return:

{0: 7, 1: 4}

Alternatively, one can employ a non-NumPy method using collections.Counter:

<code class="python">import collections, numpy

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

counter = collections.Counter(y)

print(counter)</code>

This approach also returns a dictionary with the same key-value pairs as the numpy.unique method:

Counter({0: 7, 1: 4})

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