R help - Aug 2010 - finding max value in a row and reporting colum name

Hi,

Hopefully someone can point me in the right direction on how I would go
about solving the following.

I have some data and need to find the column name of the maximum value in
each row.

This could be the data...
> a <- data.frame(x = rnorm(4), y = rnorm(4), z = rnorm(4)) 
> a
           x           y          z
1  1.6534561  0.11523404  0.2261730
2 -1.2274320 -0.24096054  1.5096028
3 -1.4503096  0.07227427  1.6740867
4  0.1867416  1.25318913 -0.7350560

Here is what I need to generate...

1 x
2 z
3 z
4 y

Any pointers would be appreciated.

Regards,



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pdb <philb <at> philbrierley.com> writes:
> 
> 
> Hi,
> 
> Here is what I need to generate...
> 
> 1 x
> 2 z
> 3 z
> 4 y
> 
> Any pointers would be appreciated.
> 
> Regards,
> 

this should work, probably other options are possible

a <- data.frame(x = rnorm(4), y = rnorm(4), z = rnorm(4)) 

z<-apply(a,1,which.max)
names(a)[z]

a <- data.frame(x = rnorm(4), y = rnorm(4), z =
rnorm(4))
> names(a)[apply(a, 1, which.max)]
[1] "y" "z" "z"
"y"
> a
           x          y          z
1 -0.8839957 -0.8824065 -0.9343157
2  0.3918695  1.4246880  1.6401349
3 -0.4020719  0.1342691  0.8041808
4  0.1500775  0.8966310 -0.2204660

HTH,
Dennis

On Sun, Aug 1, 2010 at 3:00 AM, pdb <philb@philbrierley.com> wrote:
>
> Hi,
>
> Hopefully someone can point me in the right direction on how I would go
> about solving the following.
>
> I have some data and need to find the column name of the maximum value in
> each row.
>
> This could be the data...
>
> > a <- data.frame(x = rnorm(4), y = rnorm(4), z = rnorm(4))
> > a
>           x           y          z
> 1  1.6534561  0.11523404  0.2261730
> 2 -1.2274320 -0.24096054  1.5096028
> 3 -1.4503096  0.07227427  1.6740867
> 4  0.1867416  1.25318913 -0.7350560
>
> Here is what I need to generate...
>
> 1 x
> 2 z
> 3 z
> 4 y
>
> Any pointers would be appreciated.
>
> Regards,
>
>
>
> --
> View this message in context:
>
http://r.789695.n4.nabble.com/finding-max-value-in-a-row-and-reporting-colum-name-tp2309358p2309358.html
> Sent from the R help mailing list archive at Nabble.com.
>
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> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

pdb wrote:
> 
> Hi,
> 
> Hopefully someone can point me in the right direction on how I would go
> about solving the following.
> 
> I have some data and need to find the column name of the maximum value in
> each row.
> 
> This could be the data...
> 
>> a <- data.frame(x = rnorm(4), y = rnorm(4), z = rnorm(4)) 
>> a
>            x           y          z
> 1  1.6534561  0.11523404  0.2261730
> 2 -1.2274320 -0.24096054  1.5096028
> 3 -1.4503096  0.07227427  1.6740867
> 4  0.1867416  1.25318913 -0.7350560
> 
> Here is what I need to generate...
> 
> 1 x
> 2 z
> 3 z
> 4 y
> 
> Any pointers would be appreciated.
> 
> Regards,
> 
> 
> 
> 
as.data.frame(cbind(row.names(a),apply(a,1,function(x)
names(a)[which(x==max(x))])))

LB
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