How to set numpy array value based on previous value?

Question

Example:

a = np.array([1, 0, 2, 0, 3, 4])

Goal:

Set value to 0 if the previous value is 0

Desired output:

[1, 0, 0, 0, 0, 4]

Mad Physicist · Accepted Answer · 2021-05-24 17:10:15Z

2

Make a mask of the locations that are zero:

m = (a == 0)

Apply the mask to a shifted slice of the array:

a[1:][m[:-1]] = 0

In some cases, you may want to shift by incrementing the indices:

i = np.flatnonzero(m[:-1]) + 1
a[i] = 0

answered May 24, 2021 at 17:10

Mad Physicist

116k29 gold badges202 silver badges292 bronze badges

Sign up to request clarification or add additional context in comments.

1 Answer 1