[R] Faster alternative to by?
michael watson (IAH-C)
michael.watson at bbsrc.ac.uk
Wed Jul 26 14:41:31 CEST 2006
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
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?
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