xxxxxxxxxx
x = np.array([1., -1., -2., 3])
x[x < 0] = 20
x
Output:
array([ 1., 20., 20., 3.])
xxxxxxxxxx
import numpy as np
arr = np.array([1, 2, 3, 4, 5])
mask = np.array([True, False, True, False, False])
result = arr[mask]
print(result)
[1 3]