How to select the row with the maximum value in each group

Question

In a dataset with multiple observations for each subject I want to take a subset with only the maximum data value for each record. For example, with a following dataset:

Answer 1

I wasn't sure what you wanted to do about the Event column, but if you want to keep that as well, how about

isIDmax <- with(dd, ave(Value, ID, FUN=function(x) seq_along(x)==which.max(x)))==1
group[isIDmax, ]

#   ID Value Event
# 3  1     5     2
# 7  2    17     2
# 9  3     5     2

Here we use ave to look at the "Value" column for each "ID". Then we determine which value is the maximal and then turn that into a logical vector we can use to subset the original data.frame.