sorry, I still have a question. What is the difference between an empty vector and a vector of length 0?
When I assign x<-c() is.null(x) is TRUE x<-integer(0) is.null(x) is FALSE Duncan Murdoch-2 wrote: > > Rnewbie wrote: >> dear all, >> >> I tried to use grep to match IDs in two dataframes >> >> grep(DF1$ID[i], DF2$ID) >> >> I wanted to use condition in a loop, but I have the problem to define >> what >> is in return if a match is not found. I used mode() and class() to >> compare >> between the attributes when a match is found and not found, but the mode >> and >> class are the same in both cases, numeric and integer, respectively. >> >> When a match is not found, grep returns "integer(0)". Is.numeric() and >> Is.integer() of the return gave TRUE but arithmetic calculation is not >> possible. >> > See the Value section of the ?grep man page. By default, R returns a > vector of indices of entries in x that match the pattern. Since you > have no matches, you get a vector of length 0. That is printed as > integer(0). (This is also the function call that would create a vector > of length 0.) > > One simple test for no results is length(grep(...)) == 0. > > Duncan Murdoch >> For example, >> If a match is not found for i=12, >> >> grep(DF1$ID[12], DF2$ID) returns "integer(0)" and >> >> grep(DF1$ID[12], DF2$ID)+10 returns "numeric(0)" >> >> I will appreciate any suggestions. Thanks in advance. >> >> >> > > ______________________________________________ > 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. > > -- View this message in context: http://www.nabble.com/what-is-returned-if-a-match-is-not-found-using-grep-tp24914127p24916597.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
