[R] Warning message with aggregate function

[Xingwang Ye]

Dear all,
When I use aggregate function as:

attach(warpbreaks)
aggregate(warpbreaks[, 1], list(wool = wool, tension = tension), sum)

The results are right but I get a warning message:
"number of items to replace is not a multiple of replacement length."

BTW: I use R version 2.4.1 in Ubuntu 7.04.

Your kind solutions will be great appreciated.

Best wishes

Yours, sincerely,
Xingwang Ye