MATLAB Central Newsreader - find function

find function

Branko — Mon, 05 Jan 2009 13:00:05 -0500

Let's say that I have a random matrix:
A=ceil(randn(10,1));
and I want to find -1 and 2 values in the matrix. Which is done by following command
a=find(A==-1);
b=find(A==2);
However I' d like to use single command which in this case is:
c=find(A==-1 & A==2);
But I got empty matrix.Where is the cache.
Thanks.

Re: find function

tpl@eng.cam.ac.uk (Tim Love) — Mon, 05 Jan 2009 13:06:28 -0500

"Branko" <branko_b@hotmail.com> writes:

>Let's say that I have a random matrix:
>A=ceil(randn(10,1));
>and I want to find -1 and 2 values in the matrix. Which is done by following command
>a=find(A==-1);
>b=find(A==2);
>However I' d like to use single command which in this case is:
>c=find(A==-1 & A==2);
>But I got empty matrix.Where is the cache.
The catch? You need OR, not AND, so you need | rather than &

Re: find function

Jiro Doke — Mon, 05 Jan 2009 13:09:01 -0500

"Branko" <branko_b@hotmail.com> wrote in message <gjt08k$mt1$1@fred.mathworks.com>...
> Let's say that I have a random matrix:
> A=ceil(randn(10,1));
> and I want to find -1 and 2 values in the matrix. Which is done by following command
> a=find(A==-1);
> b=find(A==2);
> However I' d like to use single command which in this case is:
> c=find(A==-1 & A==2);
> But I got empty matrix.Where is the cache.
> Thanks.

That's because a number cannot be both -1 AND 2. Are you perhaps looking for either -1 OR 2?

Then do

c = find(A==-1 | A==2);

jiro

Re: find function

us — Mon, 05 Jan 2009 13:10:20 -0500

"Branko"
> A=ceil(randn(10,1));
> and I want to find -1 and 2 values in the matrix. Which is done by following command
> c=find(A==-1 & A==2);
> But I got empty matrix.Where is the cache...

one of the solutions

m=ceil(randn(10,1));
r=find(m==-1 | m==2)
% r = 4 9 % <- based on random data...

us

Re: find function

Matt Fig — Mon, 05 Jan 2009 13:13:02 -0500

Look at the | operator.

Re: find function

Loren Shure — Tue, 06 Jan 2009 12:50:28 -0500

In article <gjt08k$mt1$1@fred.mathworks.com>, branko_b@hotmail.com
says...
> Let's say that I have a random matrix:
> A=ceil(randn(10,1));
> and I want to find -1 and 2 values in the matrix. Which is done by following command
> a=find(A==-1);
> b=find(A==2);
> However I' d like to use single command which in this case is:
> c=find(A==-1 & A==2);
> But I got empty matrix.Where is the cache.
> Thanks.
>

will ismember help you out?

--
Loren
http://blogs.mathworks.com/loren