[Rd] Should as.complex(NaN) -> NA?

[Charles C. Berry]

On Wed, 31 Mar 2010, William Dunlap wrote:

> I'm having trouble grokking complex NaN's.
> This first set examples using complex(re=NaN,im=NaN)
> give what I expect
>  > Re(complex(re=NaN, im=NaN))
>  [1] NaN
>  > Im(complex(re=NaN, im=NaN))
>  [1] NaN
>  > Arg(complex(re=NaN, im=NaN))
>  [1] NaN
>  > Mod(complex(re=NaN, im=NaN))
>  [1] NaN
>  > abs(complex(re=NaN, im=NaN))
>  [1] NaN
> and so do the following
>  > Re(complex(re=1, im=NaN))
>  [1] 1
>  > Im(complex(re=1, im=NaN))
>  [1] NaN
>  > Re(complex(re=NaN, im=1))
>  [1] NaN
>  > Im(complex(re=NaN, im=1))
>  [1] 1
> but I don't have a good mental model that explains
> why the following produce NA instead of NaN.

Just a guess here:

> as.complex(sqrt(as.complex(-1)))
[1] 0+1i
> as.complex(sqrt(-1))
[1] NA
Warning message:
In sqrt(-1) : NaNs produced

It protects from assuming that the latter truly is not a number.

Chuck


>  > as.complex(NaN)
>  [1] NA
>  > Im(complex(modulus=NaN, argument=NaN))
>  [1] NA
>  > Re(complex(modulus=NaN, argument=NaN))
>  [1] NA
>  > Re(1i * NaN)
>  [1] NA
>  > Im(1i * NaN)
>  [1] NA
>  > Re(NaN + 1i)
>  [1] NA
>  > Im(NaN + 1i)
>  [1] NA
>
> It may be that if as.complex(NaN), and its C equivalent,
> were changed to return complex(re=NaN,im=NaN) then the
> arithmetic examples would return NaN.  Is there a
> better way for me to model how NaN's in complex numbers
> should work or is this a bug?
>
> While I was looking into this I noticed a bug in str():
>  > str(NA_complex_)
>  Error in FUN(X[[1L]], ...) : subscript out of bounds
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
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>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901