[R] Subset and order at the same time?

[Berend Hasselman]

On 12-05-2012, at 20:04, Noah Silverman wrote:

> Is there a way to order data and subset it at the same time??
> 
> 
> 
> I want to sort all the members of group A by their values in column 3. (I'll then do the same for each subsequent group.)  This could be done in a loop building up another vector, but I like to avoid loops in R.
> -------------------------------------
> a <- temp[temp$group=="A",]
> a <- a[order(a[,3]),]
> temp[temp$group=="A",] <- a
> ------------------------------------------
> 
> Iid like to do this in a single step for each group.  However, I can't figure out how to order and subset at the same time.
> 
> This *does not work* but should illustrate what I'm trying to do
> 
> temp[temp$group=="A",] <- temp[ temp$group=="A" & order(temp[temp$group=="A",3]) , ]
> 
> 
> Suggestions?

set.seed(413)

temp <- data.frame(group=rep(c("A","B","C"), rep=5), tt=1:15,val=round(runif(15),2), stringsAsFactors=FALSE)
idx <- order(temp$group,temp$val)
# or   idx <- order(temp[,1],temp[,3])
idx
z2 <- temp[idx,]
rownames(z2) <- NULL
z2

Possible NA's etc. not taken into account.

Berend