Thread Subject: finding the row of a particular number in a matrix

Hi,
I have a matrix and I find the max value in particular column and then I want to know what row that number is in. Could someone please advise on how to do this?
Thanks,
Pia

"Pia " <p.sartor@sheffield.ac.uk> wrote in message <hc4320$o4$1@fred.mathworks.com>...
> Hi,
> I have a matrix and I find the max value in particular column and then I want to know what row that number is in. Could someone please advise on how to do this?
> Thanks,
> Pia

My first piece of advice is that you should carefully read

>> doc max

which shows you how to call the function MAX with two output arguments, one of which gives the location of the maximum. If you cannot figure it out from that, then I suggest you post the code you have so far, so that we can provide better guidance.

"the cyclist" <thecyclist@gmail.com> wrote in message <hc45j2$9o5$1@fred.mathworks.com>...
> "Pia " <p.sartor@sheffield.ac.uk> wrote in message <hc4320$o4$1@fred.mathworks.com>...
> > Hi,
> > I have a matrix and I find the max value in particular column and then I want to know what row that number is in. Could someone please advise on how to do this?
> > Thanks,
> > Pia
>
> My first piece of advice is that you should carefully read
>
> >> doc max
>
> which shows you how to call the function MAX with two output arguments, one of which gives the location of the maximum. If you cannot figure it out from that, then I suggest you post the code you have so far, so that we can provide better guidance.

Here is one way, although maybe not the most elegant. But it does scale nicely to N-dimensions.

h=rand(5,5); % this will be the matrix that we want to find the max.
P=reshape(h,numel(h) ,1); % convert h into 1D matrix.
[yoki,Aindex]=max(P); % find index corresponding to max point in 1D
[xIndex,yIndex]=ind2sub(size(h),Aindex); % find 2D indices of max.

"Matt Fetterman" <mattinjersey@yahoo.com> wrote in message
news:hc4hh3$f6d$1@fred.mathworks.com...
> "the cyclist" <thecyclist@gmail.com> wrote in message
> <hc45j2$9o5$1@fred.mathworks.com>...
>> "Pia " <p.sartor@sheffield.ac.uk> wrote in message
>> <hc4320$o4$1@fred.mathworks.com>...
>> > Hi,
>> > I have a matrix and I find the max value in particular column and then
>> > I want to know what row that number is in. Could someone please advise
>> > on how to do this?
>> > Thanks,
>> > Pia
>>

>> My first piece of advice is that you should carefully read
>>
>> >> doc max
>>
>> which shows you how to call the function MAX with two output arguments,
>> one of which gives the location of the maximum. If you cannot figure it
>> out from that, then I suggest you post the code you have so far, so that
>> we can provide better guidance.
>


> Here is one way, although maybe not the most elegant. But it does scale
> nicely to N-dimensions.
>
> h=rand(5,5); % this will be the matrix that we want to find the max.
> P=reshape(h,numel(h) ,1); % convert h into 1D matrix.
> [yoki,Aindex]=max(P); % find index corresponding to max point in 1D
> [xIndex,yIndex]=ind2sub(size(h),Aindex); % find 2D indices of max.

But would it not be a bit simpler to use max as suggested and take advatange
of its return values as follows?

h=rand(5,5)
[val,c]=max(h,[],1);
[val,r]=max(val);

fprintf('Max is at row=%d, column=%d\n',c(r),r)

--Nasser

"Nasser M. Abbasi" <nma@12000.org> wrote in message
news:qAnFm.32582$eJ4.26608@newsfe07.iad...
>
> "Matt Fetterman" <mattinjersey@yahoo.com> wrote in message
> news:hc4hh3$f6d$1@fred.mathworks.com...
>> "the cyclist" <thecyclist@gmail.com> wrote in message
>> <hc45j2$9o5$1@fred.mathworks.com>...
>>> "Pia " <p.sartor@sheffield.ac.uk> wrote in message
>>> <hc4320$o4$1@fred.mathworks.com>...
>>> > Hi,
>>> > I have a matrix and I find the max value in particular column and then
>>> > I want to know what row that number is in. Could someone please
>>> > advise on how to do this?
>>> > Thanks,
>>> > Pia
>>>
>
>>> My first piece of advice is that you should carefully read
>>>
>>> >> doc max
>>>
>>> which shows you how to call the function MAX with two output arguments,
>>> one of which gives the location of the maximum. If you cannot figure it
>>> out from that, then I suggest you post the code you have so far, so that
>>> we can provide better guidance.
>>
>
>
>> Here is one way, although maybe not the most elegant. But it does scale
>> nicely to N-dimensions.
>>
>> h=rand(5,5); % this will be the matrix that we want to find the max.
>> P=reshape(h,numel(h) ,1); % convert h into 1D matrix.
>> [yoki,Aindex]=max(P); % find index corresponding to max point in 1D
>> [xIndex,yIndex]=ind2sub(size(h),Aindex); % find 2D indices of max.
>

> But would it not be a bit simpler to use max as suggested and take
> advatange of its return values as follows?
>
> h=rand(5,5)
> [val,c]=max(h,[],1);
> [val,r]=max(val);
>
> fprintf('Max is at row=%d, column=%d\n',c(r),r)
>
> --Nasser

Another way, which may be even better (finds all positions of the maximum
value)

[r,c]=find(h==max(max(h)))

--Nasser