Numpy array value change via two index sets

Question

I am trying to achieve the following:

    # Before
    raw = np.array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

    # Set values to 10
    indice_set1 = np.array([0, 2, 4])
    indice_set2 = np.array([0, 1])
    raw[indice_set1][indice_set2] = 10

    # Result
    print(raw)
    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

But the raw values remain exactly the same.

Expecting this:

    # After
    raw = np.array([10, 1, 10, 3, 4, 5, 6, 7, 8, 9])

by doing raw[indice_set1] you generate a new array, which is the one you modify with the second slicing — mozway
– mozway, Commented Dec 15, 2022 at 13:55
raw[indice_set1] = 10 would change the original one to -> array([10, 1, 10, 3, 10, 5, 6, 7, 8, 9]) How can I add second layer of indexing? — arapEST
– arapEST, Commented Dec 15, 2022 at 13:58

mozway · Accepted Answer · 2022-12-15 14:03:32Z

3

After doing raw[indice_set1] you get a new array, which is the one you modify with the second slicing, not raw.

Instead, slice the slicer:

raw[indice_set1[indice_set2]] = 10

Modified raw:

array([10,  1, 10,  3,  4,  5,  6,  7,  8,  9])

answered Dec 15, 2022 at 14:03

mozway

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3 Comments

arapEST Over a year ago

Fantastic, you are better than chatGPT.

mozway Over a year ago

@arapEST given all the very bad chatGPT answers that have flooded the site lately, I hope so :p

arapEST Over a year ago

By the way that example was copied straight out of the chatGPT convo :) But, on some other cases I've got a lot of useful correct solutions from that bot.

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