Select only the first row when merging data frames with multiple matches

Question

I have two data frames, \"data\" and \"scores\", and want to merge them on the \"id\" column:

data = data.frame(id = c(1,2,3,4,5),
                  state =          


        

Answer 1

In base you can use match to Select only the first row when merging data frames with multiple matches.

#Return also those which found no match
(tt <- cbind(data, score=scores[match(data$id, scores$id),"score"]))
#  id state score
#1  1    KS    66
#2  2    MN    86
#3  3    AL    76
#4  4    FL    NA
#5  5    CA    NA

#Return only those which found a match
tt[!is.na(tt$score),]
#  id state score
#1  1    KS    66
#2  2    MN    86
#3  3    AL    76