On 04/07/18 00:24, Martin Møller Skarbiniks Pedersen wrote:
Hi,
I am currently using R v3.4.4 and I just discovered this:
prod(NA, NaN) ; prod(NaN, NA)
[1] NA
[1] NaN
?prod says:
If ‘na.rm’ is ‘FALSE’ an ‘NA’ value in any of the arguments will
cause a value of ‘NA’ to be returned, otherwise ‘NA’ values are
ignored.
So according to the manual-page for prod() NA should be returned in both
cases?
However for sum() is opposite is true:
sum(NA, NaN) ; sum(NaN, NA)
[1] NA
[1] NA
?sum says:
If ‘na.rm’ is ‘FALSE’ an ‘NA’ or ‘NaN’ value in any of the
arguments will cause a value of ‘NA’ or ‘NaN’ to be returned,
otherwise ‘NA’ and ‘NaN’ values are ignored.
Maybe the manual for prod() should say the same as sum() that
both NA and NaN can be returned?
But:
> sum(NA,NaN)
[1] NA
> sum(NaN,NA)
[1] NA
so sum gives NA "both ways around". Perhaps a slight inconsistency
here? I doubt that it's worth losing any sleep over, however.
Interestingly (???):
> NaN*NA
[1] NaN
> NA*NaN
[1] NA
> NaN+NA
[1] NaN
> NA+NaN
[1] NA
So we have an instance of non-commutative arithmetic operations. And
sum() is a wee bit inconsistent with "+".
Again I doubt that the implications are all that serious.
cheers,
Rolf Turner
--
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276
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