Replicate values in a matrix i-1 times

I want to create a new array that duplicates the first value of A, then the rest of the values (i-1) times. For example,

A=[1; 4; 8; 3; 2; 6]

I want

B=[1; 4; 8; 8; 3; 3; 3; 2; 2; 2; 2; 6; 6; 6; 6; 6]

My first attempt was a for loop but I couldn't make it work. My other idea is to do C=repmat(A,1,6) and then pull out B=[C(1,1); C(2,1); C(3,1); C(3,2); ..... etc] but I don't know how to automate this, since my actual A has 2000 values.

Any help is appreciated! Thanks.

Answer 1

[David Hill]

B=repelem(A,[1,1:5]);

[Fabio Freschi]

Nice!

Answer 2

[Fabio Freschi]

Quick and dirty for loop

A=[1; 4; 8; 3; 2; 6]

B = [];
for i = 1:length(A)
    B = [B; repmat(A(i),i,1)];
end

You can also play a bit to allocate correctly B outside the loop. It's a nice exercise