randomly change numpy array values

Question

I have an array data.

import numpy as np

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

print(data)

If some non_zero elements (1,2,3,4) have more than 5 counts, I want to randomly extract and keep 5 positions and replace all other positions into 0s.

uniques, counts = np.unique(data, return_counts=True)
for unique, count in zip(uniques, counts):
    print (unique, count)

    if count > 5:       
       
       ids = np.random.choice(range(count), 5, replace=False)

How can I do it?

Keep just 5 positions or all positions of unique, non-zero elements when their counts are more than 5? — Alex Douglas
– Alex Douglas, Commented Jul 29, 2020 at 17:33
its to keep just 5 positions, if their counts are more than 5. — Roman
– Roman, Commented Jul 29, 2020 at 17:34

yao99 · Accepted Answer · 2020-07-29 17:56:08Z

3

uniques, counts = np.unique(data, return_counts=True)
for unique, count in zip(uniques, counts):
    print (unique, count)
    if unique != 0 and count > 5:
       ids = np.random.choice(count, count-5, replace=False)
       data[tuple(i[ids] for i in np.where(data == unique))] = 0

answered Jul 29, 2020 at 17:56

yao99

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3 Comments

Roman Over a year ago

what would be an alternative to this line, data[tuple(i[ids] for i in np.where(data == unique))] = 0?

Roman Over a year ago

I could not understand that line

yao99 Over a year ago

maybe this one more easily to understand, x,y = np.where(data == unique) for i in ids: data[x[i],y[i]] = 0

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