Counting occurences of an item in an ndarray based on multiple conditions?

Question

How do you specify multiple conditions in the np.count_nonzero function.

This is for counting the numbers inside an array that have a value between two values. I know you can subtract the outcomes of two individual count_nonzero lines. But I would like to know if there is an easy way to pass multiple conditions to np.count_nonzero.

import numpy as np

array = np.array([[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
                  [0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0],
                  [0, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 0],
                  [0, 1, 1, 2, 3, 3, 3, 3, 3, 3, 3, 3, 2, 1, 1, 0],
                  [0, 1, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 3, 2, 1, 0],
                  [0, 2, 3, 4, 5, 6, 6, 6, 6, 6, 6, 5, 4, 3, 2, 0],
                  [0, 2, 3, 4, 5, 6, 7, 8, 8, 7, 6, 5, 4, 3, 2, 0],
                  [0, 2, 3, 4, 5, 6, 6, 6, 6, 6, 6, 5, 4, 3, 2, 0],
                  [0, 1, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 3, 2, 1, 0],
                  [0, 1, 1, 2, 3, 3, 3, 3, 3, 3, 3, 3, 2, 1, 1, 0],
                  [0, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 0],
                  [0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0],
                  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
                  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]])

# Count occurences of values between 5 and 8  in array.
result1 = np.count_nonzero(array <= 8)
result2 = np.count_nonzero(array <= 5)
result = result 1 - result2

I would like to know if there is a way that looks something like:

np.count_nonzero(array >= 6 and array <= 8)

zipa · Accepted Answer · 2019-10-16 11:47:42Z

5

Can this be what you are looking for:

np.count_nonzero(np.logical_and(array>=5, array<=8))
#24

answered Oct 16, 2019 at 11:47

zipa

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1 Comment

Jozef Over a year ago

That's exactly what I was looking for. I tried your method and found that np.count_nonzero actually counts the number of True inside an array, the np.logical_and returns an array with booleans and also works. Thanks!

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