Thread Subject: sub-min

Hi everyone,

I have two 2-dim arrays, A and C. C is zeros and ones.
I and want to find min(A, [ ] , 2), but only considering elements that
are ones in matrix C.

Do you know a fast way to compute this in matlab?

Thank you!
Ross

On Feb 18, 7:43 pm, Ross <fed.ro...@gmail.com> wrote:
> Hi everyone,
>
> I have two 2-dim arrays, A and C. C is zeros and ones.
> I and want to find min(A, [ ] , 2), but only considering elements that
> are ones in matrix C.
>
> Do you know a fast way to compute this in matlab?
>
> Thank you!
> Ross

ok, I guess I will go with the brute force:

a = max(max(A));
Ca = C.*a;
Amin = min(Ca+A,[ ],2);

Ross <fed.rossi@gmail.com> wrote in message
<b21b9772-12c9-4842-a58e-34c1fc28faff@v3g2000hsc.googlegroups.com>...
> On Feb 18, 7:43 pm, Ross <fed.ro...@gmail.com> wrote:
> > Hi everyone,
> >
> > I have two 2-dim arrays, A and C. C is zeros and ones.
> > I and want to find min(A, [ ] , 2), but only considering
elements that
> > are ones in matrix C.
> >
> > Do you know a fast way to compute this in matlab?
> >
> > Thank you!
> > Ross
>
> ok, I guess I will go with the brute force:
>
> a = max(max(A));
> Ca = C.*a;
> Amin = min(Ca+A,[ ],2);
>

B = A ; % work on a copy
B(C==0) = Inf ;
Amin = min(B,[],2)

hth
Jos

Ross:
<SNIP jiggling ones and zeros...

> I have two 2-dim arrays, A and C. C is zeros and ones.
> I and want to find min(A, [ ] , 2), but only considering
elements that are ones in matrix C...

i looked at previous solutions in this thread - but still
don't understand what you want...
can you tell CSSM how the output of these exemplary
matrices should look like (assuming i understand your <two
2-dim> correctly)...

     a=[
          10 20
          30 30
          50 50
     ];
     c=[
          1 0
          1 1
          0 0
     ];

us

On Feb 19, 1:58 am, "Jos " <DEL...@jasenDEL.nl> wrote:
> Ross <fed.ro...@gmail.com> wrote in message
>
> <b21b9772-12c9-4842-a58e-34c1fc28f...@v3g2000hsc.googlegroups.com>...
>
>
>
> > On Feb 18, 7:43 pm, Ross <fed.ro...@gmail.com> wrote:
> > > Hi everyone,
>
> > > I have two 2-dim arrays, A and C. C is zeros and ones.
> > > I and want to find min(A, [ ] , 2), but only considering
> elements that
> > > are ones in matrix C.
>
> > > Do you know a fast way to compute this in matlab?
>
> > > Thank you!
> > > Ross
>
> > ok, I guess I will go with the brute force:
>
> > a = max(max(A));
> > Ca = C.*a;
> > Amin = min(Ca+A,[ ],2);
>
> B = A ; % work on a copy
> B(C==0) = Inf ;
> Amin = min(B,[],2)
>
> hth
> Jos

Hi Jos,
thank you for your message
I tried this method too, and I saw that matlab spends a lot of time
with this code. Maybe it is because the A matrix is huge or it is
sparse

On Feb 19, 2:16 am, "us " <u...@neurol.unizh.ch> wrote:
> Ross:
> <SNIP jiggling ones and zeros...
>
> > I have two 2-dim arrays, A and C. C is zeros and ones.
> > I and want to find min(A, [ ] , 2), but only considering
>
> elements that are ones in matrix C...
>
> i looked at previous solutions in this thread - but still
> don't understand what you want...
> can you tell CSSM how the output of these exemplary
> matrices should look like (assuming i understand your <two
> 2-dim> correctly)...
>
> a=[
> 10 20
> 30 30
> 50 50
> ];
> c=[
> 1 0
> 1 1
> 0 0
> ];
>
> us

Hi us, thanks for replying.
To be more precise, c is a matrix of zeros and ones such that sum(c,[],
2)>0
To follow your example, and adding a one to c so that c(3,1)=1,
the output would be d = [10 30 50]'

On Feb 19, 10:32 am, Ross <fed.ro...@gmail.com> wrote:
> On Feb 19, 2:16 am, "us " <u...@neurol.unizh.ch> wrote:
>
>
>
> > Ross:
> > <SNIP jiggling ones and zeros...
>
> > > I have two 2-dim arrays, A and C. C is zeros and ones.
> > > I and want to findmin(A, [ ] , 2), but only considering
>
> > elements that are ones in matrix C...
>
> > i looked at previous solutions in this thread - but still
> > don't understand what you want...
> > can you tell CSSM how the output of these exemplary
> > matrices should look like (assuming i understand your <two
> > 2-dim> correctly)...
>
> > a=[
> > 10 20
> > 30 30
> > 50 50
> > ];
> > c=[
> > 1 0
> > 1 1
> > 0 0
> > ];
>
> > us
>
> Hi us, thanks for replying.
> To be more precise, c is a matrix of zeros and ones such that sum(c,[],
> 2)>0
> To follow your example, and adding a one to c so that c(3,1)=1,
> the output would be d = [10 30 50]'

ok, I just discovered accumarray, which solves the problem