MATLAB Vectorization help?

I have the indexes of an array in an array. While that may sound confusing, all I want to do is take the array

[ 1 2 .004
2 3 .02
3 4 .7
2 4 .01
4 5 .006]

and create the array

[0 .004 0 0 0
0 0 .02 0 0
0 0 0 .7 0
0 0 0 0 .006]

elegantly in MATLAB without for loops.

2012-10-17T14:35:07Z

Ha! Thanks, that's a little TOO elegant, this was just an example I made up . . . the array indices are not necessarily along the diagonal, this just happened to be a special case. Say the first row of the first matrix was 1 4 .004 . . . What I'm looking for is a faster version of this

for i=1:length(M(:,1))
L(M(i,1),M(i,2))=M(i,3)
end

2012-10-17T14:35:08Z

Ha! Thanks, that's a little TOO elegant, this was just an example I made up . . . the array indices are not necessarily along the diagonal, this just happened to be a special case. Say the first row of the first matrix was 1 4 .004 . . . What I'm looking for is a faster version of this

for i=1:length(M(:,1))
L(M(i,1),M(i,2))=M(i,3)
end

2012-10-17T14:37:23Z

You're also right in that I didn't mean to delete any of the rows . . .

R G2012-10-18T08:33:47Z

Favorite Answer

a=[ 1 2 .004
2 3 .02
3 4 .7
2 4 .01
4 5 .006];

% cant remember a nicer way without loops

m_size=max(a(:,1:2)); % maximum size of the future matrix
out=zeros(m_size);
ind=sub2ind(m_size,a(:,1), a(:,2));
out(ind)=a(:,3);

10

mallie2016-12-24T19:19:02Z

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