Expanding a Matrix with Repmat/Reshape?

I have two vectors:

x = [3 6 7 10]

y = [2 2 2 4]

I am trying to create vector

z = [3 3 6 6 7 7 10 10 10 10]

So each element x(i) is repeated y(i) times. This is straight forward with a for loop, but I'm trying to avoid looping, if possible. The size and values of x and y may change as well (they are populated by variables).

Here's the loop version:

    z= [];
    for i = 1:numel(y)
        z= [z, repmat(x(i), 1, y(i))];
    end

Any help is appreciated.

Answer 1

[James Tursa]

E.g.,

z = cell2mat(cellfun(@(x,y)repmat(x,1,y),num2cell(x),num2cell(y),'Uni',false));

But this just hides the loops in the background.

Answer 2

[Steven Lord]

If you're using release R2015a or later, use repelem.

x = [3 6 7 10];
y = [2 2 2 4];
z = repelem(x, y)

Answer 3

[Matt J]

Here's a truly loop free method,

   clear p

   p(cumsum(y,'reverse'))=1;

   z=x(cumsum(flip(p)))

Answer 4

[Jan]

x = [3 6 7 10]
y = [2 2 2 4]
z = repelem(x, y);

Or if this is the bottleneck of your code, try FEX: RunLength:

Z = RunLength(x, y);