[R] How to force aggregate to exclude NA ?

[hadley wickham]

>> aggregate(m[,-c(1:2)], by=list(m[,1]), mysum)   <----------------- this computes correctly.
>  Group.1  C  D
> 1       A  3  2
> 2       B 15 13
> 3       C 10 10
> 4       D  6  7
> 5       E  9  8
>
>> aggregate(m[,-c(1:2)], by=list(m[,1]), mylength) <----------------- this computes correctly.
>  Group.1 C D
> 1       A 1 1
> 2       B 5 4
> 3       C 3 4
> 4       D 2 3
> 5       E 4 4
>
> There are other statistics I need to compute e.g. var, sd, and it is a hassle to create customized versions to exclude NA. Any alternative approaches ?

How about writing a function to do the customisation for you?

na.rm <- function(f) {
  function(x, ...) f(x[!is.na(x)], ...)
}

aggregate(m[,-c(1:2)], by=list(m[,1]), na.rm(sum))
aggregate(m[,-c(1:2)], by=list(m[,1]), na.rm(length))

Hadley

-- 
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