# Alternation without for loop

3 views (last 30 days)
JamJan on 15 Oct 2019
Commented: J. Alex Lee on 15 Oct 2019
I have 2 vectors that I want to alternate
A = [1 2 3 4 5 6 7 8 9 10]
B = [0.5 0.2 0.4 0.8 0.9]
I would like to have the following output (preferably without for loop)
Output = [1 0.5 2 0.2 3 0.4 4 0.8 5 0.9 6 7 8 9 10]
How to do this?
Thanks!

Stephen Cobeldick on 15 Oct 2019
Edited: Stephen Cobeldick on 15 Oct 2019
>> N = min(numel(A),numel(B));
>> V = [reshape([A(1:N);B(1:N)],1,[]),A(N+1:end),B(N+1:end)]
V =
1 0.5 2 0.2 3 0.4 4 0.8 5 0.9 6 7 8 9 10

#### 1 Comment

J. Alex Lee on 15 Oct 2019
nice...i like when i didn't see the obvious complete opposite path...and i learned a new thing with the empty argument for reshape

Jos (10584) on 15 Oct 2019
% a sorting trick
A = [1 2 3 4 5 6 7 8 9 10]
B = [0.5 0.2 0.4 0.8 0.9]
C = [A B] ;
[~,ix] = sort([1:numel(A) 1:numel(B)])
C = C(ix)

J. Alex Lee on 15 Oct 2019
Here's a possibility: if A and B were guaranteed to be the same length (your example is not) and row vectors, you could do
N = length(A)
Output = reshape([A(:),B(:)]',2*N,1)
If not same length, you can nan-pad the shorter vector and remove later.

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