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From: Elizabeth on 31 Mar 2010 09:40
If I have a matrix x:
x=[1 2 3;4 5 6;7 8 9;10 11 12];

and i wanted to delete rows 1 and 2 then i can do
ab=[1,2];
x[ab,:]=[];

and rows 1 and 2 would be deleted.
But what if I wanted to delete all rows EXCEPT 1 and 2.

This is a simplified example, as what I actually have is x with a length of over a thousand rows, but I want to delete all but 60 or so of them, but the principle is still the same.

thanks
From: us on 31 Mar 2010 09:49
"Elizabeth " <elizabeth.robertson(a)eee.strath.ac.uk> wrote in message <hovjc6$oqn$1(a)fred.mathworks.com>...
> If I have a matrix x:
> x=[1 2 3;4 5 6;7 8 9;10 11 12];
>
> and i wanted to delete rows 1 and 2 then i can do
> ab=[1,2];
> x[ab,:]=[];
>
> and rows 1 and 2 would be deleted.
> But what if I wanted to delete all rows EXCEPT 1 and 2.
>
> This is a simplified example, as what I actually have is x with a length of over a thousand rows, but I want to delete all but 60 or so of them, but the principle is still the same.
>
> thanks

one of the solutions

m=magic(4);
kx=[2,4];
m=m(kx,:) % <- just KEEP those, rather then REMOVE them...
%{
% m =
5 11 10 8
4 14 15 1
%}

us
From: ImageAnalyst on 31 Mar 2010 09:50
How about this:

x = [1 2 3;4 5 6;7 8 9;10 11 12]
keeperRows = [1,2]
allRows = 1:size(x,1)
rowsToDelete = setxor(keeperRows, allRows)
x(rowsToDelete,:)=[]

You could cram it all into a single line if you wanted to be compact
(and a bit harder to understand) instead of verbose/descriptive.
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