[R] find max value in each row and return column number and column name

[David Winsemius]

On Nov 1, 2013, at 10:03 AM, Gary Dong wrote:

> Dear R users,
> 
> I wonder how I can use R to identify the max value of each row, the column
> number column name:
> 
> For example:
> 
> a <- data.frame(x = rnorm(4), y = rnorm(4), z = rnorm(4))
> 
>> a
>           x          y          z
> 1 -0.7289964  0.2194702 -2.4674780
> 2  1.0889353  0.3167629 -0.9208548
> 3 -0.6374692 -1.7249049  0.6567313
> 4 -0.1348642  0.4507473 -1.7309010
> 
> In this data frame, I compare y and z only.
> 
> What I need:
> 
>          x                     y                 z            max         max.col.num         max.col.name
> 1 	-0.7289964 	 0.2194702 	-2.4674780         0.2194702               2
>                     y
> 2  1.0889353  0.3167629 -0.9208548         0.3167629               2
>                     y
> 3 -0.6374692 -1.7249049  0.6567313         0.6567313               3
>                    z
> 4 -0.1348642  0.4507473 -1.7309010         0.4507473               2
>                    y
> 
> 
> Any suggestion will be greatly appreciated!

cbind(a, max=apply(a,1,max),
         max.col.num =apply(a,1,which.max) ,
         max.col.name= names(a)[apply(a,1,which.max)]  )
> 
> Thank you!
> 
> Gary
> 
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David Winsemius
Alameda, CA, USA