creating a vector from a bin count

Hello,

I have a matrix I got from another source that look like:

[0 5; 1 2; 2 1]

I wish to get a vector like [0 0 0 0 0 1 1 2] .

Thanks

EC

Answer 1

[Stephen23]

R2015a or later:

>> M = [0 5; 1 2; 2 1];
>> repelem(M(:,1),M(:,2)).'
ans =
     0     0     0     0     0     1     1     2

R2014b or earlier:

>> C = arrayfun(@(x,n)repmat(x,1,n),M(:,1),M(:,2),'uni',0);
>> [C{:}]
ans =
     0     0     0     0     0     1     1     2

[einat covo]

Thank you!

Answer 2

[Rik]

You could of course do this with a loop (or cellfun), but I think a more elegant solution is with cumsum instead.

data=[0 5; 1 2; 2 1];

delta=data(:,1)-[0;data(1:(end-1),1)];
change_pos=[0;cumsum(data(1:(end-1),2))]+1;
out=accumarray(change_pos,delta);
out=cumsum(out);

The idea in this code is to do this:

%repeat 0 for 4 entries, 1 for 1 entry, and don't repeat 2
[0 x x x x 1 x 2]
%by setting x to 0, cumsum will create the desired matrix