MATLAB: ‘reshape’ by identifiers

reshape

Hi, I am trying to reshape data by two identifiers: date and id. The origianl data I have can be simplified as follow;
date id v1
2000 1  99
2001 1  84
1997 2  74
1998 2  89
1999 2  48
2000 2  43
2001 2  45
2002 2  49
And I need to change the original data into the matrix as below;
date id1 id2
1997  .  74
1998  .  89
1999  .  48
2000 99  43
2001 84  45
2002  .  49
I used to use nested for loop that goes through every elemnt in the original data and copy it into the matrix I need to generate if both of date and id are matched. But now, the length of original data is over 3 mil and it took me more than 30 min. to make the matrix I want. And I don't think plain reshape function can solve this problem. Can anyone help me to solve this problem? Thank you.
Minsoo

Best Answer

This should probably be much faster:
[uyear, m, yearidx] = unique(Matrix(:,1));
OutMat = nan(length(uyear),3);
OutMat(:,1) = uyear(:);
OutMat(sub2ind([length(OutMat),3], yearidx, 1 + Matrix(:,2))) = Matrix(:,3);
(Function corrected as the output of the previous iteration required a reshape())
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