How to get the maximum value by group

Question

I have a data.frame with two columns: year and score. The years go from 2000-2012 and each year can be listed multiple times. In the s

Answer 1

using base packages

> df
  year score
1 2000    18
2 2001    22
3 2000    21
> aggregate(score ~ year, data=df, max)
  year score
1 2000    21
2 2001    22

EDIT

If you have additional columns that you need to keep, then you can user merge with aggregate to get those columns

> df <- data.frame(year = c(2000, 2001, 2000), score = c(18, 22, 21) , hrs = c( 10, 11, 12))
> df
  year score hrs
1 2000    18  10
2 2001    22  11
3 2000    21  12
> merge(aggregate(score ~ year, data=df, max), df, all.x=T)
  year score hrs
1 2000    21  12
2 2001    22  11