Two equal max values in R

Question

I have a dataframe with some numbers(score) and repeating ID. I want to get the maximum value for each of the ID. I used this function

top = aggregate(df$score, list(df$ID),max)

This returned me a top dataframe with maximum values corresponding to each ID.

But it so happens that for one of the ID, we have two EQUAL max value. But this function is ignoring the second value.

Is there any way to retain BOTH the max values.?

For Example:

df

ID   score
1    12
1    15
1    1
1    15
2    23
2    12
2    13

The above function gives me this: top

ID    Score
1     15
2     23

I need this: top

ID   Score
1    15
1    15
2    23

Answer 1

I recommend data.table as Chris mentioned (good for speed, but steeper learning curve). Or if you don't want data.table you could use plyr:

library(plyr)
ddply(df, .(ID), subset, score==max(score))
# same as ddply(df, .(ID), function (x) subset(x, score==max(score)))

Answer 2

You can convert to a data.table:

DT <- as.data.table(df)
DT[, .SD[score == max(score)], by=ID]