Try: rbind(v2,unname(setNames(v1[,1],v1[,2])[v2])) [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14] v2 "a" "a" "a" "a" "a" "c" "c" "c" "c" "c" "c" "c" "c" "c" "1" "1" "1" "1" "1" "3" "3" "3" "3" "3" "3" "3" "3" "3" [,15] [,16] [,17] [,18] v2 "c" "b" "b" "b" "3" "2" "2" "2" A.K.
Hi, I have a matrix of unique elements (strings) like v1 and a vector which contains replicated values of the 2nd column of the first matrix. v1 = cbind(c("1","2","3"),c("a","b","c")) v2 = c(rep("a",5), rep("c",10), rep("b",3)) How can I add a column to v2 that contains the values of the first column of the first matrix v1 where the 2nd column of v1 matches the values of v2? Do I need to grep by looping over the nrow of v1 which is very time consuming or is there a better solution? the results should be the same as v3=rbind( c(rep("a",5), rep("c",10), rep("b",3)), c(rep("1",5), rep("3",10), rep("2",3))) --------------------------------------------------------------- v1 [,1] [,2] [,3] [1,] "1" "2" "3" [2,] "a" "b" "c" > v2 [1] "a" "a" "a" "a" "a" "c" "c" "c" "c" "c" "c" "c" "c" "c" "c" "b" "b" "b" > v3 [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14] [1,] "a" "a" "a" "a" "a" "c" "c" "c" "c" "c" "c" "c" "c" "c" [2,] "1" "1" "1" "1" "1" "3" "3" "3" "3" "3" "3" "3" "3" "3" [,15] [,16] [,17] [,18] [1,] "c" "b" "b" "b" [2,] "3" "2" "2" "2" ______________________________________________ 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.