Duplicating a column vector into a longer column vector

Question

Starting with A = [3;4;5], I want to duplicate it six times to get A =[3;3;3;3;3;3;4;4;4;4;4;4;5;5;5;5;5;5].

I can think of some brute force ways to do it, but looking for something optimized since this will be run through a loop many times.

possible duplicate of A similar function to R's rep in Matlab — Dan
– Dan, Commented Jan 14, 2014 at 6:23

Stewie Griffin · Accepted Answer · 2013-11-10 17:42:35Z

4

How about using kron? It's very suited for this purpose.

kron(A,ones(6,1))

answered Nov 10, 2013 at 17:42

Stewie Griffin

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Luis Mendo · Accepted Answer · 2013-11-10 19:27:20Z

Yet another possibility, which involves no arithmetical operations:

reshape(repmat(A,1,6).',[],1);

However, if you really need speed, and if the A vector size is the same in all iterations of the loop, it's best to precompute (outside the loop) an indexing vector like this

ind = reshape(repmat([1;2;3],1,6).',[],1);

and then within the loop you only need to do

A(ind)

Franck Dernoncourt · Accepted Answer · 2013-11-10 17:35:00Z

0

A = [3;4;5]; duplicate_factor = 6; A = reshape((A*(ones(duplicate_factor,1))')', [], 1)

answered Nov 10, 2013 at 17:35

Franck Dernoncourt

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