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SQL like question.
From: |
John W. Eaton |
Subject: |
SQL like question. |
Date: |
Fri, 05 Sep 2008 14:00:24 -0400 |
On 5-Sep-2008, Levente Torok wrote:
| Hi All,
|
| Last time Jaroslav helped me a lot with a little trick but this time I am a
little bit jammed.
|
| I would like to get solved a simple thing again and I cannot find a fast
solution to it.
|
| I have a matrix as
| m = [
| 1 2;
| 1 1;
| 2 3;
| 2 4 ];
|
| I would like to make a unique of its first column but I would like to have
the minimum of second column nearby.
| So it would look like:
| [ 1 1;
| 2 3 ]
|
| This is something like SELECT first_col, min(second_col) FROM m GROUP BY
first_col;
|
| If I can be sure that the second nargout of unique() always points always to
the last index of the same
| selector item then the solution would be something like:
|
| m = sort( m, 'descend' );
| [u,i,j] = unique( m(:,1) );
| m(i,:)
|
| but
| 1) can I be sure about it?
| 2) what if I would want to make aggregate functions such as avg() or var()
I think the help list might be a better place for questions like
this. I'd really like to keep discussions on the maintainers list
focused on development issues.
Thanks,
jwe