[R] 2 simple questions
Uwe Ligges
ligges at statistik.uni-dortmund.de
Fri May 6 17:42:30 CEST 2005
sms13+ at pitt.edu wrote:
> Please excuse what I'm sure are very easy questions but I'm relatively
> new to the R environment.
> How can I view a range of list elements, but not all. e.g., I had a
> matrix of patients and then split them out by patient id. I know I can
> do patlist[[1]] to see the first one, but how can I view, say, the first
> ten patients?
Use vector indexing on patlist such as
patlist[1:10]
which return a list of the first 10 elements.
Please read the docs on object indexing.
> My other question is how to count how many patients have a record in
> which a certain condition holds. E.g., I was trying something like this
> to get a count:
> ctr<-0
> temp<-lapply(mylist, function(x){is.na(x$date1[1]) & !is.na(x$date2[1]))
> ctr<-ctr+1})
No, lapply is NOT a loop, instead think vectorized:
## at first look at a logical vector, where the condition holds:
temp <- sapply(mylist, function(x)
(is.na(x$date1[1]) & !is.na(x$date2[1])))
ctr <- sum(temp) # and sum that vector
Uwe Ligges
> But I don't think that's working correctly.
>
> Thanks,
> Steven
>
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