How to extend a array by multiplying internal values e.g. [1 2 3 4] to [1 1 1 2 2 2 3 3 3 4 4 4]?

How can I extend this array:

A = [1 2 3 4 5 6 7]

So that a new array can be formed in which each value of array A appears 4 times, and the array keeps its order? E.g. for array A the result would be:

B = [1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 7]

Thanks for any advice :)

Answer 1

[Roger Stafford]

   B = A(ceil((1:4*size(A,2))/4));   % <--- Corrected

Answer 2

[Sean de Wolski]

B = kron(A,ones(1,4))

Or

B = reshape(repmat(A,4,1),1,[])

[Jan]

According to the definition of the problem kron() is the direct solution in a mathematical manner. From the view point of a software engineer, the numerical multiplication is an indirection here and repmat avoids them. Therefore I prefer both solutions.

Answer 3

[Stephen23]

I don't know how this compares for speed, but it gets the desired result using some basic MATLAB matrix multiplication:

>> A = [1 2 3 4 5 6 7];
>> B = [1;1;1;1] * A;
>> B = B(:).'
ans = [1  1  1  1  2  2  2  2  3  3  3  3  4  4  4  4  5  5  5  5  6  6  6  6  7  7  7  7]

Answer 4

[Azzi Abdelmalek]

A = [1 2 3 4 5 6 7]
B=bsxfun(@times,ones(4,1),A);
out=B(:)'

[Sean de Wolski]

I'd expect

bsxfun(@plus,zeros(4,1),A)

to be faster.

[Azzi Abdelmalek]

Exact, but the repmat solution is faster