How to set numpy array value based on previous value?

user_12488445 0
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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]
indexing numpy python
1 Answers

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
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