numpy-数组的复杂修改

Question

Suppose I have a int16 numpy array such as:

 ([[ 1, 1, 1, 1, 1, 1, 1],

   [ 1, 0, 1, 1, 1, 1, 1],

   [ 0, 0, 0, 1, 1, 1, 0],

   [ 1, 0, 0, 0, 0, 1, 0],

   [ 0, 1, 0, 0, 0, 1, 0]])

I'd like to modify this array so that every 1 with a 0 in the space directly below it becomes a 21. I'd also like to do this on multiple, much larger arrays. What is the fastest way to carry this out?

Answer 1

Assuming the last row is supposed to stay the same you can to the following.

sel = (A[:-1] == 1) * (A[1:] == 0)
A[:-1][sel] = 21

Here A is your matrix. The first line creates a masked array of size (m - 1, n) with m, n = A.shape .