creating a vector from a bin count

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einat covo
einat covo 2019-5-23
回答： Rik 2019-5-23
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

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采纳的回答

Stephen23
Stephen23 2019-5-23
编辑：Stephen23 2019-5-23
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

更多回答（1 个）

Rik
Rik 2019-5-23
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

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