Hi
I have a data.frame, two columns, 12304 rows. Both columns are factors.
I want to do an equivalent of an SQL "group by" statement, and count the
number of rows in the data frame for each unique value of the second
column.
I have:
countl <- by(mapped, mapped$col2, nrow)
Now, mapped$col2 has 10588 levels, so this statement takes a really long
time to run. Is there a more efficient way of doing this in R?
Thanks
Mick