# Construct a vector from another, but add 2 values every 10 iteration

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V.D-C on 11 Jan 2020
Commented: V.D-C on 11 Jan 2020
Hello !
I would like to create a vector B from a vector A, and at every 10th iteration, implement 2 times the same value from A:
A = linspace(0,1,811);
B = [];
for i = 1:1:length(A)
if mod(i,10) ~= 0
B = [B,A(1,i)];
elseif mod(i,10) == 0
end
end
I know the length of the vector B should be around 901. I should have 90 "added_values", but when I verify it I have almost 1000 of them.
And it seems at every iteration the "if" condition just skips to the "elseif" part... What should I do to make this work ? I can't think of any other method...

Meg Noah on 11 Jan 2020
Try this:
npts = 811;
A = linspace(0,1,npts);
k = 0;
for i = 1:1:npts
k = k + 1;
B(k) = A(1,i);
if mod(i,10) == 0
k = k + 1;
B(k) = A(1,i);
end
end
% another way to do it...
npts = 811;
A = linspace(0,1,npts);
idx = 1:npts;
idxRepeat = find(mod(1:npts,10) == 0);
idxA2B = sort([idx idxRepeat]);
B = A(idxA2B);
V.D-C on 11 Jan 2020
You just solved 2 days of intense failures, I can't thank you enough !!!