Selecting rows that are the same in separate data frames
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
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