Hi Gabor, thanks a lot. I understand it now. But Andrew's method is easier for me to understand. Can I extend my question? I have a data file, every line has such format: 2:102 5:85 ... The number before colon is data entry index, the number after colon is data entry value, and other data entries are zero. I use scan to read them in R and need to separate the index and value to different vectors. For example:
> foo [1] "2:102" "5:85" > foo2 <- strsplit(foo, split=":") > foo2 [[1]] [1] "2" "102" [[2]] [1] "5" "85" > myIndex <- as.numeric(unlist(lapply(foo2, function(x) x[1]))) or > myIndex <- as.numeric(foo2, "[", 1) > myIndex [1] "2" "5" Is this the simplest way to get the index or value vector? -Luke On 5/16/05, Gabor Grothendieck <[EMAIL PROTECTED]> wrote: > Its the indexing function written in ordinary function form. That is, > foo[1:2] can be written as "["(foo, 1:2) > > On 5/16/05, Luke <[EMAIL PROTECTED]> wrote: > > Yes, it works. Althought I can understand the help page of sapply, I > > don't know why it works. What is "["? > > > > -Luke > > > > On 5/16/05, Gabor Grothendieck <[EMAIL PROTECTED]> wrote: > > > On 5/16/05, Luke <[EMAIL PROTECTED]> wrote: > > > > I have a simple question, but I couldn't find the answer in R manuals. > > > > > > > > Assume I have a list: > > > > > foo <- list() > > > > > foo[[1]] <- c(1, 2, 3) > > > > > foo[[2]] <- c(11,22,33) > > > > > foo[[3]] <- c(111,222,333) > > > > > foo > > > > [[1]] > > > > [1] 1 2 3 > > > > > > > > [[2]] > > > > [1] 11 22 33 > > > > > > > > [[3]] > > > > [1] 111 222 333 > > > > > > > > How to use list index to get a vector of, say, the first elements of > > > > list elements? > > > > That is, how to get a vector c(1, 11, 111) from foo? > > > > > > > > foo[[]][1] doesn't work. > > > > > > > > > > Try this: > > > > > > sapply(foo, "[", 1) > > > > > > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html