R help - Mar 2006 - returning the largest element in an array/matrix?

Hi all,

I want to use "which.max" to identify the maximum in a 2D array/matrix
and I
want "argmin" and return the row and column indices.

But "which.max" only works for vector...

Is there any convinient way to solve this problem?

Thanks a lot!

	[[alternative HTML version deleted]]

indcol <- rep(1:ncol(mat), each=nrow(mat))[which.max(mat)]
indrow <- rep(1:nrow(mat), ncol(mat))[which.max(mat)]


indrow <- which(apply(mat==max(mat),1,sum)!=0)
indcol <- which(apply(mat==max(mat),2,sum)!=0)


Michael a ?crit :
>Hi all,
>
>I want to use "which.max" to identify the maximum in a 2D
array/matrix and I
>want "argmin" and return the row and column indices.
>
>But "which.max" only works for vector...
>
>Is there any convinient way to solve this problem?
>
>Thanks a lot!
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>
>  
>

Try this:

m <- diag(4-abs(-4:4))  # test matrix
wm <- which.max(m)
c(row(m)[wm], col(m)[wm])   # c(5,5)

On 3/6/06, Michael <comtech.usa at gmail.com>
wrote:
> Hi all,
>
> I want to use "which.max" to identify the maximum in a 2D
array/matrix and I
> want "argmin" and return the row and column indices.
>
> But "which.max" only works for vector...
>
> Is there any convinient way to solve this problem?
>
> Thanks a lot!
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

Hi

If you do not insist on which.max() you can use

which(mat==max(mat), arr.ind=T)

HTH
Petr




On 6 Mar 2006 at 20:55, Michael wrote:

Date sent:      	Mon, 6 Mar 2006 20:55:20 -0800
From:           	Michael <comtech.usa at gmail.com>
To:             	R-help at stat.math.ethz.ch
Subject:        	[R] returning the largest element in an array/matrix?
> Hi all,
> 
> I want to use "which.max" to identify the maximum in a 2D
array/matrix
> and I want "argmin" and return the row and column indices.
> 
> But "which.max" only works for vector...
> 
> Is there any convinient way to solve this problem?
> 
> Thanks a lot!
> 
>  [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
Petr Pikal
petr.pikal at precheza.cz