[R] 2 simple questions

[Uwe Ligges]

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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