[R] sum in vector

Hadley Wickham hadley at rice.edu
Wed Nov 17 16:35:05 CET 2010

> rowsum(value, paste(factor1, factor2, factor3))

That is dangerous in general, and always inefficient. Imagine factor1
is c("a", "a b") and factor2 is ("b c", "c").  Use interaction with
drop = T.


Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University

More information about the R-help mailing list