# How can I find each character's index within a matrix, from a vector of characters?

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Mackenna Landis on 28 Apr 2023
Answered: DGM on 28 Apr 2023
I have a matrix of characters
Letters = [A, B, C;
D, E, F;
G, H, I];
Secondarily, I will have a vector of letters, and I need to find the index of each letter in the matrix of Letters. For example,
vec = [A, C, H, I], or it could be any combination of letters. I'm sure there is a simple answer that I am missing. I know normally you need to call the character with a string, but I don't know how to call, say vec(1) as a string (as in, idx = find(Letters == vec(1)), and it would return 1, for A), which I think would solve the problem.

Chunru on 28 Apr 2023
Letters =['ABC'; 'DEF'; 'GHI']
Letters = 3×3 char array
'ABC' 'DEF' 'GHI'
vec = 'ACHI'
vec = 'ACHI'
for i=1:length(vec)
[r, c] = find(Letters == vec(i));
fprintf("%s: (%d, %d)\n", vec(i), r, c)
end
A: (1, 1) C: (1, 3) H: (3, 2) I: (3, 3)

DGM on 28 Apr 2023
If you're talking strictly about character arrays, then:
Letters = ['ABC'; 'DEF'; 'HIJ'];
vec = 'ACHI';
[~, idx] = ismember(vec,Letters) % idx is a linear index into Letters
idx = 1×4
1 7 3 6

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