ave reports a warning here:
> DF <- data.frame(A = c(1, 2, 2), B = c(1, 1, 2), C = c(1, 2, 3))
> with(DF, ave(C, A, B, FUN = min))
[1] 1 2 3
Warning message:
In FUN(X[[4L]], ...) : no non-missing arguments to min; returning Inf
In this case it can be avoided by using drop = TRUE which could only
be discovered by looking at the source code and at any rate should not
be necessary:
> with(DF, ave(C, A, B, drop = TRUE, FUN = min))
[1] 1 2 3
The problem is that internally ave uses interaction(...) -- in the
example above that would correspond to interaction(A, B). This can
result in a factor with unused levels. Replacing interaction(...)
in the source code with
interaction(..., drop = TRUE)
would avoid the warning message.
> ave
function (x, ..., FUN = mean)
{
n <- length(list(...))
if (n) {
g <- interaction(...)
split(x, g) <- lapply(split(x, g), FUN)
}
else x[] <- FUN(x)
x
}
<environment: namespace:stats>
> R.version.string
[1] "R version 2.12.1 Patched (2010-12-16 r53864)"
I got the same results with:
> R.version.string
[1] "R version 2.13.0 Under development (unstable) (2011-02-11 r54330)"
>
--
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com
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