Add one to an array at list of indices using numpy

Asked May 23 '20 at 13:20

Active May 23 '20 at 14:08

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I have a 2D array, a, and another array, index_list, that is a list of valid indices for that 2D array. The same index may appear more than once. I want to add one to that 2D array at every index that appears in the list of indices. If an index appears n times, I want to add one n times.

For example, given:

a = np.arange(9).reshape((3,3))
index_list = np.array([[0,0],[0,1],[2,2],[2,2]])

I want a function to return:

[[1,2,2],
 [3,4,5],
 [6,7,10]]

How can I do this with just numpy?

asked May 23 '20 at 13:20

BlewbsTart

1

`np.add.at` can handle the duplicate index as you want. – hpaulj May 23 '20 at 14:04
Thank you, this does exactly what I want. – BlewbsTart May 23 '20 at 14:11
Does this answer your question? [np.add.at indexing with array](https://stackoverflow.com/questions/45473896/np-add-at-indexing-with-array) – Joe May 23 '20 at 14:31

Add one to an array at list of indices using numpy

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