[R] Aggregate to find majority level of a factor

[Thompson, Jonathan]

I want to use the aggregate function to summarize data by a factor (my
field plots), but I want the summary to be the majority level of another
factor.

 
For example, given the dataframe:

Plot1     big
Plot1     big
Plot1     small
Plot2     big
Plot2     small    
Plot2     small
Plot3     small
Plot3     small
Plot3     small


My desired result would be:
Plot1 big
Plot2 small
Plot3 small


I can't seem to find a scalar function that will give me the majority
level. 

Thanks in advance,

Jonathan Thompson