Avoiding for loop with ismember

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Christian
Christian 2017-6-23
编辑： Andrei Bobrov 2017-6-23
Hi, suppose N is a scalar, and c is a numerical vector with unique elements that are a subset of 1:N, i.e. its size is smaller or equal to N. For example, N=4, and c=[1 2 4]'; Then, is there a more elegant way to achieve this?
cc = [];
for j = 1:N
if ismember(j,c)
cc = [cc; N*(j-1)+c];
end
end
Thanks!
  2 个评论
Stephen23
Stephen23 2017-6-23
What do you expect the output cc to be?
Christian
Christian 2017-6-23
If N=4, and c=[1 2 4]'; then cc is going to be [1 2 4 5 6 8 13 14 16]'.

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2017-6-23
编辑：Andrei Bobrov 2017-6-23
[Fixed]
N = 15;
c = randperm(N,4);
c1 = sort(c(:));
cc = reshape(bsxfun(@plus,N*(c1 - 1),c1')',[],1);
or
oc = ones(numel(c1),1);
cc = N*(kron(c1,oc) - 1) + kron(oc,c1);
or
c = c(:);
nn = numel(c);
cc = N*(repelem(c,nn) - 1) + repmat(c,nn,1);
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Stephen23
Stephen23 2017-6-23
@Christian: With the data you have shown us cc will definitely be a matrix. If c is a column vector then you should specify this in your question.
Christian
Christian 2017-6-23
I think that gives the right result. I wish it was more readable / elegant.

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