On 1/12/2009, at 8:32 PM, Karl Ove Hufthammer wrote:
SNIP
Exercise to the reader:
Note that
sapply(split(x, ff, drop=TRUE), sum)
gives you the values of (just) the non-empty levels.
Now, why does
sapply(split(x, ff), sum, drop=TRUE)
give the wrong value (1) for these levels, while
On Tue, 1 Dec 2009 14:10:17 +1300 Rolf Turner r.tur...@auckland.ac.nz
wrote:
Consider the following:
set.seed(42)
ff - factor(sample(c(1,3,5),42,TRUE),levels=1:5)
x - runif(42)
tapply(x,ff,sum)
12345
3.675436 NA 7.519675 NA
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