Suppose you have an array:
And lets say you add 20 to everything
[ 20, 21, 20]
[ 19, 22, 21]
[ 23, 16, 22]
Now lets say I want to add the resulting
b to the original array
a but only in cases where
a < 0 i.e at the index
a = -1, -4 respectively getting the value 0 otherwise. Ultimately leading to a matrix as such:
[ 0, 0, 0]
[ 18, 0, 0]
[ 0, 12, 0]
18 = 19 (from b) + -1 (from a)
12 = 16 (from b) + -4 (from a)
And assume that I want to be able to extend this to any operation (not just add 20), so that you can’t just filter all values < 20 from matrix
c. So I want to use matrix
a as a mask toward matrix c, zeroing the
i, j where
a[i,j] < 0.
I’m having a tough time finding a concise example of how to do this in numpy with python. I was hoping you may be able to direct me to the correct implementation of such a method.
What I am struggling to get is this into a mask and only performing operations on the retained values, finally resulting in
Thanks for the help in advance.
Probably something like:
(a + b)*(a<0)
should work unless you have very strong requirements concerning the number of intermediate arrays.