Re: extracting elements

[Mike Miller]

On Sat, 30 Apr 2005, Steve C. Thompson wrote:

> How about this:
>
> I=[1,2,5,4]';              % desired rows
> J=[1,3;2,4;1,4;2,3];       % desired columns
> X=reshape([1:20],4,5)';    % matrix to pull elements from
>
> X1=X';
>
> [Jr,Jc]=size(J);
> [X1r,X1c]=size(X1);
>
> a=(I-1)*X1r*ones(1,Jc);
> Y=X1(J+a)


Thanks, Steve!  Is that the same as this?:

X(I*ones(1,size(J,2))+size(X,1)*(J-1))

It took me awhile, but that's what I came up with.

Let's see...

size(X,1)=X1c
size(J,2)=Jc

X(I*ones(1,Jc)+X1c*(J-1))

Well, it's hard to figure out.  Your use of the transpose is throwing me 
off.  If they both give the same answer, that's good enough for me!

Thanks again.

Mike



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------