> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Leeds, Mark (IED) > Sent: Thursday, October 11, 2007 12:34 PM > To: [EMAIL PROTECTED] > Subject: [R] confusion with R syntax > > I just noticed something by accident with R syntax that I'm sure is > correct but I don't understand it. If I have > a simple numeric vector x and I subscript it, it seems that I can then > subscript a second time with TRUE > or FALSE, sort of like a 2 dimensional array in C. Does > someone know if > this is documented somewhere > Because it's neat but I never knew it existed. To me it seems like a 1 > dimensional vector should > have only one dimensional indexing ? > > x <- seq(1,10) > > x > [1] 1 2 3 4 5 6 7 8 9 10 > > x[2:4][c(TRUE,FALSE,TRUE)] > [1] 2 4 > > But, it only works for TRUE or FALSE and not numbers so I > think it's not > really 2 dimensional indexing. > > x[1][2] > > [1] NA > > If someone could explain this mechanism or tell me what I should look > for in the archives, it would > be appreciated. Thanks.
Mark, Indexing with numbers works the same as with logicals. The problem with your example > x[1][2] is that x[1] returns a single value, but your are then asking for the second value which is NA. Try the following >x[2:4][2] Hope this is helpful, Dan Daniel J. Nordlund Research and Data Analysis Washington State Department of Social and Health Services Olympia, WA 98504-5204 ______________________________________________ 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.
