Is this, from the man page, relevant? "An empty index selects all values: this is most often used to replace all the entries but keep the attributes. "
Bert Gunter Genentech Nonclinical Statistics -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Barry Rowlingson Sent: Friday, March 26, 2010 5:10 AM To: r-help@r-project.org Subject: [R] NA values in indexing If you index a vector with a vector that has NA in it, you get NA back: > x=101:107 > x[c(NA,4,NA)] [1] NA 104 NA > x[c(4,NA)] [1] 104 NA All well and good. ?"[" says, under NAs in indexing: When extracting, a numerical, logical or character 'NA' index picks an unknown element and so returns 'NA' in the corresponding element of a logical, integer, numeric, complex or character result, and 'NULL' for a list. (It returns '00' for a raw result.] But if the indexing vector is all NA, you get back a vector of length of your original vector rather than of your index vector: > x[c(NA,NA)] [1] NA NA NA NA NA NA NA Maybe it's just me, but I find this surprising, and I can't see it documented. Bug or undocumented feature? Apologies if I've missed something obvious. Barry sessionInfo() R version 2.11.0 alpha (2010-03-25 r51407) i686-pc-linux-gnu locale: [1] LC_CTYPE=en_GB.UTF-8 LC_NUMERIC=C [3] LC_TIME=en_GB.UTF-8 LC_COLLATE=en_GB.UTF-8 [5] LC_MONETARY=C LC_MESSAGES=en_GB.UTF-8 [7] LC_PAPER=en_GB.UTF-8 LC_NAME=C [9] LC_ADDRESS=C LC_TELEPHONE=C [11] LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C attached base packages: [1] stats graphics grDevices utils datasets methods base ______________________________________________ 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.
