accumulating unique indices in array

Dear All,

I have a vector A = [1;1;2;4;2;7;3;2;5;4;7;1..];

I need to count the no of times each index shows in a vector B = [1;2;1;1;2;1;1;3;1;2;2;3..].

Intuitively, I think it may involve unique and accummaray, but I just cannot get it to work, thank you,

Octavian

(R2018a)

Answer 1

[Walter Roberson]

A = [1;1;2;4;2;7;3;2;5;4;7;1];
B = [1;2;1;1;2;1;1;3;1;2;2;3];

ua = unique(A);
[found, idx] = ismember(B, ua);

[ua, accumarray(idx(found), 1, [length(ua),1])]

ans = 6×2

1 6 2 4 3 2 4 0 5 0 7 0

Answer 2

[Matt J]

B = histcounts(A,1:max(A)+1)

[Octavian]

That is not working, B= [3,3,1,2,1,0,2] is different from B above; I do not need simple binning, but row to row index counts, see B above, thank you.

[Matt J]

A = [1;1;2;4;2;7;3;2;5;4;7;1];
B = [1;2;1;1;2;1;1;3;1;2;2;3];

Au=unique(A);

counts = histcounts( B(ismember(B,Au))  ,   [Au(:); Au(end)+1] );

[Au(:),counts(:)]

ans = 6×2

1 6 2 4 3 2 4 0 5 0 7 0