Repeat matrix columns in pairs.
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Hello,
I'm trying to use the repelem function to repeat some columns of a matrix A like:
A = [1 2 3 4; 5 6 7 8];
If I use the repelem function I'll get the following output:
out = repelem(A,1,2);
out =
[1 1 2 2 3 3 4 4 ; 5 5 6 6 7 7 8 8]
However I'm trying to repeat two columns at the same time instead of doing it individually. So that I get an output like:
Output = [1 2 1 2 3 4 3 4; 5 6 5 6 7 8 7 8]
Anyone can come around a solution to this problem?
Thank you,
Santos
采纳的回答
David Hill
2021-4-22
out=[repmat(A(:,1:2),1,2),repmat(A(:,3:4),1,2)];
5 个评论
Santos García Rosado
2021-4-22
David Hill
2021-4-22
out=[];
for k=2:2:size(A,2)
out=[out,repmat(A(:,k-1:k),1,2)];
end
Santos García Rosado
2021-4-22
David Hill
2021-4-22
You could reshape, not sure it will be any faster.
out=reshape(repelem(reshape(A',2,[]),1,2),2*size(A,2),[])';
Santos García Rosado
2021-4-23
更多回答（1 个）
Wolfgang
2022-6-24
Here is a more generalized solution which duplicates pairs of columns and doesn't depend on the number of columns, however the number of columns in A has to be even.
B = reshape(kron(ones(2,1), reshape(A, 2*size(A,1), [])), size(A,1), []);
This also allows to triplicate pairs of columns by using:
B = reshape(kron(ones(3,1), reshape(A, 2*size(A,1), [])), size(A,1), []);
Or you can triplicate triples of columns (number of columns in A must be a multiple of 3):
B = reshape(kron(ones(3,1), reshape(A, 3*size(A,1), [])), size(A,1), []);
Also possible: duplicate triples of columns:
B = reshape(kron(ones(2,1), reshape(A, 3*size(A,1), [])), size(A,1), []);
And so on ...
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