How to obtain all the values in a numpy array using an array containing index numbers I want to access

Question

Suppose I have the following two numpy arrays. idxes contains the indices of the elements I want to be returned from arr.

arr = ['a', 'b', 'c' ]
idxes = [1, 2]
// This is the result I'm after
result = ['b', 'c']

Initial thoughts were to use np.where and a boolean array but it seems pretty awkward to use and was wondering if there's a more elegant solution since I'm quite new to numpy.

:O I tried that with my simple example and it works perfectly but for my more complex arr, which is an array of numpy arrays with dimension (256, 256, 3) I get a TypeError: PointSelection __getitem__ only works with bool arrays. @U10-Forward's solution works for my particular numpy array tho :) — ptk
– ptk, Commented Jul 17, 2019 at 9:42

U13-Forward · Accepted Answer · 2019-07-17 09:33:28Z

2

Use this simple list comprehension which iterates through idxes and get the value with the index in idxes (i) in arr:

print([arr[i] for i in idxes])

Output:

['b', 'c']

If they're numpy arrays:

print(arr[idxes])

Output:

['b' 'c']

answered Jul 17, 2019 at 9:33

U13-Forward

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Ankur Sinha · Accepted Answer · 2019-07-17 09:42:44Z

0

Another way:

list(map(arr.__getitem__, idxes))

Output:

['b', 'c']

answered Jul 17, 2019 at 9:42

Ankur Sinha

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