repeated value of a vector

Good evening, I have a doubt that I can't solve... If I have a vector, like (1, 5, 15, 2), and I want to create another one that has every single value of the vector repeated for a certain number of times, for example 2, having as output (1, 1, 5, 5, 15, 15, 2, 2), what is the best way to do it?

I thougth of using a for cycle for each value of the vector but I don't know how.

[Chien Poon]

a = [1, 5, 15, 2]; % Your vector
b = repmat(a,2,1); % This creates a copy of the vector in the 2nd dimension
c = reshape(b,[],1)'; % We then reshape the matrix back to a vector

Answer 1

[Abolfazl Chaman Motlagh]

a naive way is to use a loop for every index:

x = [1,5,15,2];  % for example
num = 2; % number of repeat you want
index=1;
for i=1:numel(x) % numel(x) means number of elements in x
    for j=1:num
        y(index) = x(i);
        index = index + 1;
    end
end
y

y = 1×8

1 1 5 5 15 15 2 2

by simple loop you can just :

for i=1:num*numel(x) 
    y2(i) = x(ceil(i/num));
end
y2

y2 = 1×8

1 1 5 5 15 15 2 2

so for example : for both i=1 and i=2, ceil(i/2) would be 1 .

Some easier way :

y3 = repmat(x,[num 1]);
y3 = y(:)'

y3 = 1×8

1 1 5 5 15 15 2 2

the repmat, repeat your array in whatever direction you want. when i use [num 1] it repeats your array num-times in y derection and create a matrix. caling (:) for y will make the result linear in y-direction. finally by ' transpose it, so it would be a linear vector in x-direction.

[alessandro mutasci]

thank you so much! very comprehensive!!

Answer 2

[Dave B]

repelem is perfect for this kind of problem:

x = [1 5 15 2]

x = 1×4

1 5 15 2

repelem(x,2)

ans = 1×8

1 1 5 5 15 15 2 2