Stack copies of elements of a vector

Question

I have a vector that has N=1263 entries:

temp=[14, 0.5, ..., 12]

I want to make a vector which repeats entry 1, i.e. 14, 42 times, then entry 2, i.e. 0.5, 42 times and similarly all through the vector. It should produce a vector with size 53046x1.

The following code does the work for a simple case:

F = [1 4 9];
R = [repmat(F(1),[3,1]); repmat(F(2),[3,1]); repmat(F(3),[3,1])]    
R = [1 1 1 4 4 4 9 9 9]

but it is cumbersome when N becomes large. Is there a faster way around this?

Try this way: R = repmat(F(:)', 3, 1); R = R(:); – Andrei Davydov Jun 16 '17 at 10:28 — Andrei Davydov, Jun 16 '17 at 10:28

score 3 · Accepted Answer · answered Jun 16 '17 at 11:10

3

This is exactly what repelem (introduced in R2015a) is for. For your actual problem, you would use:

R = repelem(temp.',42);  %This will repeat each entry of 'temp' 42 times

For the given example,

F = [1 4 9];
R = repelem(F.',3);      %This will repeat each entry of 'F' 3 times

You can also do it with this:

R = ones(42,1)*temp;
R = R(:);

answered Jun 16 '17 at 11:10

Sardar Usama

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Also (for Matlab versions without `repelem`): `F = [1 4 9]; n = 3; R = F(ceil(1/n:1/n:end))` – Luis Mendo Jun 16 '17 at 11:29

score 1 · Answer 2 · answered Jun 16 '17 at 10:49

1

Kind of an unusual way of doing this but it works

https://www.mathworks.com/help/matlab/ref/kron.html

All you need to do is include your matrix as well as a ones matrix of the length of the repetition.

R = kron(F(:),ones(42,1));

answered Jun 16 '17 at 10:49

Durkee

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score 0 · Answer 3 · answered Jun 16 '17 at 11:05

0

R = reshape(repmat(F, 42, 1), [], 1);

answered Jun 16 '17 at 11:05

Vahe Tshitoyan

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Stack copies of elements of a vector

3 Answers3