Use the WHERE method to replace all numbers in a Numpy array with a

I'm trying to use the where method to replace all odd numbers from the below array with a -1

np.array([0, 1, 0, 3, 0, 5, 0, 7, 0, 9])

I've tried using the below, but it's not working.

np.where(Q9 % 2 == 1) = - 1

Thanks for any assistance!

CodePudding user response：

where method only returns indices

arr = np.array([0, 1, 0, 3, 0, 5, 0, 7, 0, 9])
arr[np.where(arr%2!=0)] = -1
print(arr)

output:

[ 0 -1  0 -1  0 -1  0 -1  0 -1]

CodePudding user response：

If you want to replace in the original array, where is not needed, use simple indexing:

a = np.array([0, 1, 0, 3, 0, 5, 0, 7, 0, 9])

a[a%2==1] = -1

a

For a new array:

b = np.where(a%2==1, -1, a)

output: array([ 0, -1, 0, -1, 0, -1, 0, -1, 0, -1])