[Rcpp-devel] setdiff

[Hadley Wickham]

> I've commited an initial version of setdiff.

Cool - thanks!  It might be useful in general to expose some of the
STL sorted range commands - I'm not sure if that's general enough for
base Rcpp or not.

> There is room for improvement given the R version:
>
>> setdiff
> function (x, y)
> {
>     x <- as.vector(x)
>     y <- as.vector(y)
>     unique(if (length(x) || length(y))
>         x[match(x, y, 0L) == 0L]
>     else x)
> }
>
> 'initial' because it does not yet deal with missing values correctly.
>
>
>
> Is the behavior of R's setdiff what we would want to reproduce:
>
>> setdiff( c(1), c(NA,1) )
> numeric(0)
>
> # that looks odd
>> setdiff( c(1), c(NA,2) )
> [1] 1
>
> # this too
>> setdiff( c(1,NA), c(1,2) )
> [1] NA
>
> # not sure what we should expect
>> setdiff( c(NA_integer_), c(NA_integer_) )
> integer(0)

That seems reasonable to me.  What are you thinking?

Hadley

-- 
RStudio / Rice University
http://had.co.nz/