accumulating unique indices in array

2021 2 25
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更新时间：2021 2 26
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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)

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Walter Roberson
Walter Roberson 2021-2-26
Ran in:

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Ran in:
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

更多回答（1 个）

Matt J
Matt J 2021-2-25

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

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Octavian
Octavian 2021-2-26
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
Matt J 2021-2-26
编辑：Matt J 2021-2-26
Ran in:
Ran in:
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

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