Thanks for reply. What I want is the equivalent of this :
xxx = 1:10 which(xxx %in% c(2,5)) .......but where there is more than one criterion for matching. which (b %in% a) in the code I included does nothing (not surprisingly). I'm not sure that I can use merge, because I want the whole of a, but to mark those rows which are also in b. If I do merge ( a,b ), I just get b. If I do merge ( a,b, all.x =TRUE), I get a. bartjoosen wrote: > > I'm not sure what you want, but take a look at ?merge and %in% > > > ppaarrkk wrote: >> >> I want to compare two matrices or data frames and select or get an index >> for those rows which are the same in both. I have tried the following : >> >> >> >> >> >> >> a = matrix ( 1:10, ncol = 2 ) >> a >> >> b = matrix ( c ( 2,3,4,7,8,9 ), ncol = 2 ) >> b >> >> a[a==b] >> >> >> >> >> >> >> a = as.data.frame ( matrix ( 1:10, ncol = 2 ) ) >> a >> >> b = as.data.frame ( matrix ( c ( 2,3,4,7,8,9 ), ncol = 2 ) ) >> b >> >> a[a==b] >> >> >> >> >> >> >> >> >> Any ideas please. >> >> >> Thanks. >> >> >> Simon Parker >> Imperial College >> >> > > -- View this message in context: http://www.nabble.com/Selecting-rows-that-are-the-same-in-separate-data-frames-tp20916243p20917838.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.
