On 8/25/2013 8:12 PM, Jim Lemon wrote:
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 {
for(levl in levels(by)) {
nextlags<-lags(x[by==levl],prefix=prefix)
rownames(nextlags)<-paste(levl,rownames(nextlags),sep=".")
if(exists("res")) res<-rbind(res,nextlags)
else res<-nextlags
}
}
return(res)
}
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() }.
> events <- sample(letters[1:4], 10, replace=TRUE)
> lags(events)
lag0 lag1
1 c <NA>
2 b c
3 d b
4 d d
5 b d
6 b b
7 b b
8 c b
9 a c
10 a a
> lags(events, 3)
lag0 lag1 lag2 lag3
1 c <NA> <NA> <NA>
2 b c <NA> <NA>
3 d b c <NA>
4 d d b c
5 b d d b
6 b b d d
7 b b b d
8 c b b b
9 a c b b
10 a a c b
>
> events2 <- data.frame(sub=factor(rep(1:2, each=5)),
+ event=sample(letters[1:4], 10, replace=TRUE),
+ stringsAsFactors=FALSE)
> events2
sub event
1 1 b
2 1 c
3 1 a
4 1 a
5 1 b
6 2 a
7 2 b
8 2 a
9 2 b
10 2 a
> lags(events2, 2, by=sub)
Error in lags(events2, 2, by = sub) : object 'res' not found
> lags(events2, by=sub)
Error in lags(events2, by = sub) : object 'res' not found
-Michael
--
Michael Friendly Email: friendly AT yorku DOT ca
Professor, Psychology Dept. & Chair, Quantitative Methods
York University Voice: 416 736-2100 x66249 Fax: 416 736-5814
4700 Keele Street Web: http://www.datavis.ca
Toronto, ONT M3J 1P3 CANADA
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