[R] keep the row indexes/names when do aggregate

[Gabor Grothendieck]

Rather than aggregate, use order and duplicated as in this post:

https://stat.ethz.ch/pipermail/r-help/2008-September/173139.html

On Wed, Sep 24, 2008 at 11:21 AM, zhihuali <lzhtom at hotmail.com> wrote:
>
> Hi, R-users,
>
> If I have a data frame like this:
>>x<-data.frame(g=c("g1","g2","g1","g1","g2"),v=c(1,7,3,2,8))
>   g v
> 1 g1 1
> 2 g2 7
> 3 g1 3
> 4 g1 2
> 5 g2 8
>
>
> It contains two groups, g1 and g2. Now for each group I want the max v:
>
>> aggregate(x$v,list(g=x$g),max)
>   g x
> 1 g1 3
> 2 g2 8
>
> Beautiful. But what if I want to keep the row index of (g1 3) and (g2 8) in the original x?
> So I want is:
>>do something
>   g x
>  3 g1 3
>  5 g2 8
>
> Of course it'd may make much more sense if the row indexes are some row names that I want to keep.
>
> Is there a simple way to do that?
>
> Thanks a lot!
>
> Z
>
>
>
>
>
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