On 16/05/2011, at 7:39 PM, Ketil Malde wrote:
I'm not intimately familiar with IEEE 754, but in any case we'd be in good company: R typically lets you select to sort NaNs as greater or less than any other values, and sorts non-NaN values correctly also in the presence of NaNs, I think.
sort(c(3,1,0/0,4,9)) [1] 1 3 4 9
The default behaviour is that missing (NA) and NaN values disappear from the result. There is a keyword parameter "na.last for controlling the treatment of NAs. If TRUE, missing values in the data are put last; if FALSE, they are put first; if NA, they are removed." The default value is NA. This is *not* a global property of comparison, it is specifically a run-time option of the "sort" function and the closely related "order" function, which returns a permutation vector. It is perfectly possible to provide such a feature in a specific function without violating the IEEE standard in any way, e.g. [x | x <- ys, isNaN x] ++ sort [x | x <- ys, not (isNaN x)]