Suppose I have a 3 numpy arrays
x1 = [5, 2, 3, 1, 4, 5]
x2 = [8,14,22,33,0,7]
y = [0,0,1,0,1,1]
I want to select the elements in x1 when y==0 and in x2 when y==1
output = [5,2,22,1,0,7]
What is the most efficient way ?
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3 Answers
Use numpy.where:
np.where(y, x2, x1)
Output:
array([ 5, 2, 22, 1, 0, 7])
Comments
Try masking and simple element-wise addition
import numpy as np
x1 = np.array([5, 2, 3, 1, 4, 5])
x2 = np.array([8,14,22,33,0,7])
y = np.array([0,0,1,0,1,1]).astype(bool)
output = x1*~y + x2*y
array([ 5, 2, 22, 1, 0, 7])
Comments
In case of list, instead of np.array, you can use:
[x2[i] if v else x1[i] for i,v in enumerate(y)]
#[5, 2, 22, 1, 0, 7]
