On 08/26/2013 11:44 PM, Michael Friendly wrote:
...
Thanks for trying again, but that doesn't work either with a by=
variable. Note that your function is recursive, and also k=k
should be passed in the else{ ... lags() }.
Hi Michael,
You are correct about the k=, and I had used a separate object for the
by= argument which did work. So, I tried to work around the problem of
having the by= argument look like an object with deparse(substitute())
but couldn't get it to go. However, if you can live with passing the
factor name as a string, this seems to work.
lags<-function(x,k=1,prefix='lag',by) {
if(missing(by)) {
n<-length(x)
res<-data.frame(lag0=x)
for(i in 1:k) res<-cbind(res,c(rep(NA,i),x[1:(n-i)]))
colnames(res)<-paste0(prefix,0:k)
}
else {
byfac<-factor(unlist(x[by]))
x<-x[!(names(x) %in% by)]
for(levl in levels(byfac)) {
nextlags<-lags(x[byfac==levl,],k=k,prefix=prefix)
rownames(nextlags)<-paste(levl,rownames(nextlags),sep=".")
if(exists("res")) res<-rbind(res,nextlags)
else res<-nextlags
}
}
return(res)
}
lags(events2,3,by="sub")
lag0 lag1 lag2 lag3
1.1 b <NA> <NA> <NA>
1.2 c b <NA> <NA>
1.3 c c b <NA>
1.4 d c c b
1.5 c d c c
2.1 d <NA> <NA> <NA>
2.2 c d <NA> <NA>
2.3 d c d <NA>
2.4 a d c d
2.5 a a d c
Jim
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