# Elementwise indexing of a vector by a multidimentional array

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Louis Exley on 18 Jan 2022
Answered: DGM on 18 Jan 2022
I have:
• A, an n-dimentional array of integers, whose values are in the range 1-100,
• and T, a 1-dimentional, length 100 array of values.
I want a new n-dimentional array B which, for each corresponding (same position) integer c of A, has the value T(c).
What is the proper way to do this without a for loop, preferrably that works on a gpuArray?

KSSV on 18 Jan 2022
n = 10 ;
A = randi(n,2,2,10) ;
B = rand(1,n) ;
iwant = B(A)
iwant =
iwant(:,:,1) = 0.6011 0.4264 0.6566 0.7867 iwant(:,:,2) = 0.0678 0.6011 0.2322 0.6011 iwant(:,:,3) = 0.0678 0.4264 0.2878 0.2322 iwant(:,:,4) = 0.9453 0.2322 0.6598 0.0678 iwant(:,:,5) = 0.7867 0.6598 0.9453 0.7867 iwant(:,:,6) = 0.4264 0.0678 0.5672 0.2322 iwant(:,:,7) = 0.2878 0.9453 0.0678 0.9453 iwant(:,:,8) = 0.9453 0.9453 0.6566 0.6566 iwant(:,:,9) = 0.6598 0.4264 0.6566 0.6566 iwant(:,:,10) = 0.6566 0.5672 0.5672 0.2878

DGM on 18 Jan 2022
I have no idea what's ideal for gpuArray, but this is how it would be done with linear indexing.
T = 11:20; % a vector
A = randi([1 10],2,2,2) % a 3D array
A =
A(:,:,1) = 3 8 5 2 A(:,:,2) = 10 3 6 9
B = T(A) % linear indexing
B =
B(:,:,1) = 13 18 15 12 B(:,:,2) = 20 13 16 19

R2021b

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