How to get index from value in 2D Numpy array

Question

I have two arrays:

values_arr = [[100,1], [20,5], [40,50]...[50,30]]
images_arr = [img1, img2, img3,...imgn]

Both the arrays are numpy arrays.

The values_arr and images_arr are in the same order. i.e

[100, 1] corresponds to img1

How do I get the image given the value of index?

index = [20,5]

In this case, I should get img2 given the value of index = [20,5].

You can use boolean indexing: images_arr[(values_arr == [20,5]).all(axis=1)] — user7864386
– user7864386, Commented Jan 30, 2022 at 9:59
Encode your keys into a single integer for faster lookup. What have you tried? — Mad Physicist
– Mad Physicist, Commented Jan 30, 2022 at 10:17

Yadnesh Salvi · Accepted Answer · 2022-01-30 10:12:29Z

1

You can make a dict as

values_arr_tup = [tuple(i) for i in values_arr]
dict_ = {key:value for key,value in zip(values_arr_tup ,images_arr)}

then perform dict_[tuple(index)] to get the image

answered Jan 30, 2022 at 9:58

Yadnesh Salvi

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2 Comments

TypeError: unhashable type: 'numpy.ndarray'

That is because of list cannot be key in python, so I made some changes to my answer.

sagi · Accepted Answer · 2022-01-30 10:01:08Z

1

You can use np.where to extract the index of the item :

images_arr[np.where(values_arr == [20,5])[0][0]]

answered Jan 30, 2022 at 9:55

sagi

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