How Do I Count Element Occurrences in Numpy Arrays?

Counting Occurrences in Numpy Arrays

In order to determine the frequency of specific elements within a Numpy array, various approaches exist. One common method involves utilizing the numpy.unique function. This function identifies the distinct elements in the array and returns a corresponding array of counts for each unique value.

Consider the following example array:

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

Using numpy.unique:

<code class="python">import numpy

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

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

This will output a dictionary with the unique elements (0 and 1) as keys and their corresponding counts as values.

Alternatively, a non-NumPy method using collections.Counter can be employed:

<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 will provide a Counter object with the unique elements as keys and their counts as values.

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