カウンタライブラリで配列内の要素1.頻度統計。
In [1]: import numpy as np
In [2]: from collections import Counter
In [3]: a = np.array([[1,2],[3,4]])
In [4]: Counter(a.flatten())
Out[4]: Counter({1: 1, 2: 1, 3: 1, 4: 1})
In [5]: b = np.array([[1,1],[3,4]])
In [6]: Counter(b.flatten())
Out[6]: Counter({1:2, 3: 1, 4: 1})