Re: [R] Selecting obs within groups defined by 2 variables

Hello, > > The by function does not seem to allow two variables in the Indices > argument: > Yes it does, but you must use a list of variables. (Read the help for 'by': INDICESa factor or a list of factors, each of length nrow(data).) mydata <- read.table(text=" C1 C2 C3 1 x 1 1 x 2 1

Re: [R] Selecting obs within groups defined by 2 variables

Hi Peter, Thanks! This was very helpful and worked perfectly. Naomi On Apr 4, 2012, at 4:52 PM, Peter Alspach wrote: Tena koe Naomi There are lots of ways to do this. Here are a couple (note I've made a minor modification to your example): naomi C1 C2 C3 1 1 x 1 2 1 x 2 3 1 y

Re: [R] Selecting obs within groups defined by 2 variables

Tena koe Naomi There are lots of ways to do this. Here are a couple (note I've made a minor modification to your example): > naomi C1 C2 C3 1 1 x 1 2 1 x 2 3 1 y 1 4 1 y 2 5 2 x 1 6 2 x 2 7 2 x 3 8 2 y 1 9 2 y 2 > tapply(naomi[,3], naomi[,1:2], function(x) x[length