[Rd] NaN behavior of cumsum

[Lukas Stadler]

Hi!

I noticed that cumsum behaves different than the other cumulative functions wrt. NaN values:
> values <- c(1,2,NaN,1)
> for ( f in c(cumsum, cumprod, cummin, cummax)) print(f(values))
[1]  1  3 NA NA
[1]   1   2 NaN NaN
[1]   1   1 NaN NaN
[1]   1   2 NaN NaN

The reason is that cumsum (in cum.c:33) contains an explicit check for ISNAN.
Is that intentional?
IMHO, ISNA would be better (because it would make the behavior consistent with the other functions).

- Lukas