Adding a ranking column to a dataframe
This seems like it must be a very common task, but I can't find a solution in google or SO. I want to add a column called 'rank' to 'dat1' based on the sequence that 'order.scores' applies to 'dat'. I tried using row.names(), but the rownames are based on 'dat', not 'dat1'. I also tried 'dat$rank <-rank(dat1)', but this produces an error message.
fname<-c("Joe", "Bob", "Bill", "Tom", "Sue","Sam","Jane","Ruby")
score<-c(500, 490, 500, 750, 550, 500, 210, 320)
dat<-data.frame(fname,score)
order.scores<-order(dat$score,dat$fname)
dat1<-dat[order.scores,]
Answer
You can compute a ranking from an ordering as follows:
dat$rank <- NA
dat$rank[order.scores] <- 1:nrow(dat)
dat
# fname score rank
# 1 Joe 500 5
# 2 Bob 490 3
# 3 Bill 500 4
# 4 Tom 750 8
# 5 Sue 550 7
# 6 Sam 500 6
# 7 Jane 210 1
# 8 Ruby 320 2