Add a “rank” column to a data frame

Question

I have a dataframe with counts of different items, in different years:

df <- data.frame(item = rep(c(\'a\',\'b\',\'c\'), 3),
                 year = rep(c         


        

Answer 1

Using order function,

transform(dat, x= ave(count,year,FUN=function(x) order(x,decreasing=T)))
  item year count x
1    a 2010     1 3
2    b 2010     4 2
3    c 2010     6 1
4    a 2011     3 2
5    b 2011     8 1
6    c 2011     3 3
7    a 2012     5 3
8    b 2012     7 2
9    c 2012     9 1

EDIT

You can use plyr here also:

ddply(dat,.(year),transform,x =  order(count,decreasing=T))