Fast creation of vector [0 0 1 1 2 2 3 3... n n]

Hi all,

like mentioned in the title, is there a fast way of creating a vector with repeating digits?

Thanks!

Simon

Answer 1

[per isakson]

Test

    >> reshape( cat( 1, [0:n], [0:n] ), 1, [] )
    ans =
         0     0     1     1     2     2     3     3     4     4     5     5

and

    >> reshape( repmat( [0:n], 2,1 ), 1, [] )

[Cedric]

The REPMAT solution is more efficient.

Answer 2

[Andrei Bobrov]

k = [1;1]*(0:n);
out = k(:)';

[Paul Safier]

Perfect.

Answer 3

[Jos (10584)]

n = 10 % max value
k = 3  % number of repetitions

V = floor((0:k*(n+1)-1)/k)

[Cedric]

Interestingly the RESHAPE/REPMAT solution above is faster than the FLOOR approach for k=2 and n=1e7 .. I didn't expect that.

[Jos (10584)]

Reshaping does not take a lot of time. Is it also faster for larger values of k?

[per isakson]

Is this solution immune to floating point errors?

Answer 4

[Steven Lord]

n = 5;
x1 = repelem(0:n, 2)

x1 = 1×12

0 0 1 1 2 2 3 3 4 4 5 5

[Paul Safier]

Oh wow, very nice. I'd never heard of the repelem function. Thanks.

Answer 5

[Danilo NASCIMENTO]

V=zeros(1,20);
k=0;
i=1;
while i<20
    V(i)=k;
    V(i+1)=k;
    k=k+1;
    i=i+2; 
end
V