Anna Dunietz wrote on 09/02/2011 07:16:45 AM:
>
> Hi All!
>
> Please find code and the respective lists below. My problem: I specify
the
> case that lilwin[[p]] is not an NA and want the code found in iwish to
be
> returned ONLY for that case. Why do I get a list of length 2 (and why
is
> NULL the first element)?
The list is length 2 because when p=2 in your for loop you save the output
to iwish[2]. Since nothing was saved to iwish[1] (when lilwin[[1]] was
NA) that gives a NULL value for iwish[1]. If you want to allow the length
of iwish to be shorter, you need to change the way you save your output.
For example,
iwish <- list()
count <- 0
for(p in 1:length(biglist)){
if(is.na(lilwin[[p]])==F) {
count <- count + 1
iwish[count] <- list(biglist[[p]][lilwin[[p]]])
}
}
Jean
> I understand that the code below is quite
> senseless. I have run into a problem while working on a large project
and
> wanted to simplify it in order for it to be more understandable and
> accessible. If I should not be using the if function, please let me
know
> what I should be doing instead. I know that I must use the for function
for
> my project. The thing I most want to understand is how, after
specifying a
> certain condition, one may save certain data that occurs when that
condition
> is met. I hope I have been clear enough!
>
> Thank you very much for your help!
> Anna
>
> biglist<-list(a=1:4,b=2:6)
> lilwin<-list(x=NA,y=2)
> lilloss<-list(m=1,n=3)
>
>
>
> > biglist$a
> [1] 1 2 3 4
>
> $b
> [1] 2 3 4 5 6
> > lilwin$x
> [1] NA
>
> $y
> [1] 2
> > lilloss$m
> [1] 1
>
> $n
> [1] 3
>
>
> iwish<-list()
> for(p in 1:length(biglist)){
> if(is.na(lilwin[[p]])==F) iwish[p]<-list(biglist[[p]][lilwin[[p]]])
> }
>
>
> > iwish[[1]]
> NULL
>
> [[2]]
> [1] 3
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