[R] Select top three values from data frame

[Noah Silverman]

Hi,

I'm trying to find an easy way to do this.

I want to select the top three values of a specific column in a subset 
of rows in a data.frame.  I'll demonstrate.

A    B    C
x    2    1
x    4    1
x    3    2
y    1    5
y    2    6
y    3    8


I want the top 3 values of B from the data.frame where A=X and C <2

I could extract all the rows where C<2, then sort by B, then take the 
first 3.  But that seems like the wrong way around, and it also will get 
messy with real data of over 100 columns.

Any suggestions?