How to set elemnts of numpy array based on elements of another numpy array

Question

I'm trying to set elemnts of array1 to nan based on elements of array2 which are nan.

The following is my code (which isn't working)

I would greatly appreciate assistance :)

array1 = np.array([1.,1.,1.,1.,1.,1.,1.,1.,1.,1.])
array2 = np.array([2.,2.,2.,2.,np.nan,np.nan,np.nan,2.,2.,2.])

#I want to create:
#[1.,1.,1.,1.,np.nan,np.nan,np.nan,1.,1.,1.]

# I've tried:
array1[array2 == np.nan] = np.nan
print(array1)
[1. 1. 1. 1. 1. 1. 1. 1. 1. 1.]

Answer 1

Use np.isnan.

import numpy as np
array1 = np.array([1.,1.,1.,1.,1.,1.,1.,1.,1.,1.])
array2 = np.array([2.,2.,2.,2.,np.nan,np.nan,np.nan,2.,2.,2.])
array1[np.isnan(array2)] = np.nan
print(array1)

Output is as desired:

[ 1.  1.  1.  1. nan nan nan  1.  1.  1.]

Answer 2

You can use numpy.argwhere to find the indices with np.nan and finally use those indices to change the value of array1.

import numpy as np

array1 = np.array([1.,1.,1.,1.,1.,1.,1.,1.,1.,1.])
array2 = np.array([2.,2.,2.,2.,np.nan,np.nan,np.nan,2.,2.,2.])

inds = np.argwhere(np.isnan(array2))
print(inds)
array1[inds] = np.nan

print(array1)

[[4]
 [5]
 [6]]
[ 1.  1.  1.  1. nan nan nan  1.  1.  1.]