Have you read ?"[[" ? The short answer is that you can use both [] and [[]] on lists, the [] construct will return a subset of the list (which will be a list) while [[]] will return a single element of the list (which could be a list or a vector or whatever that element may be): compare:
> tmp <- list( a=1, b=letters ) > tmp[1] $a [1] 1 > tmp[1] + 1 Error in tmp[1] + 1 : non-numeric argument to binary operator > tmp[[1]] [1] 1 > tmp[[1]] + 1 [1] 2 -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Ajay Askoolum > Sent: Thursday, January 26, 2012 11:27 AM > To: R General Forum > Subject: [R] What does [[1]] mean? > > I know that [] is used for indexing. > I know that [[]] is used for reference to a property of a COM object. > > I cannot find any explanation of what [[1]] does or, more pertinently, > where it should be used. > > Thank you. > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting- > guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.