Effacer les filtres
Effacer les filtres

Repeat matrix columns in pairs.

12 vues (au cours des 30 derniers jours)
Santos García Rosado
Santos García Rosado le 22 Avr 2021
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

Réponse acceptée

David Hill
David Hill le 22 Avr 2021
out=[repmat(A(:,1:2),1,2),repmat(A(:,3:4),1,2)];
  5 commentaires
David Hill
David Hill le 22 Avr 2021
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
Santos García Rosado le 23 Avr 2021
I'll take a good look at it. Thank you David.

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Wolfgang
Wolfgang le 24 Juin 2022
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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