[Rd] NaN behavior of cumsum

[Tomas Kalibera]

Hi Lukas,

thanks for the report. I've changed cumsum so that it is now consistent 
with cumprod wrt to NA/NaN propagation.
Now NaN is not turned into NA unnecessarily.

Still please be aware that generally NaNs may become NAs in R (on some 
platforms/compilers)
?NaN says

"Computations involving ‘NaN’ will return ‘NaN’ or perhaps ‘NA’:
which of those two is not guaranteed and may depend on the R
platform (since compilers may re-order computations)."

Best
Tomas

On 01/20/2017 02:52 PM, Lukas Stadler wrote:
> 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
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