[Rd] c(NA, 0+1i) not the same as c(as.complex(NA), 0+1i)?

[Martin Maechler]

>>>>> Michael Chirico 
>>>>>     on Mon, 6 Nov 2023 23:18:40 -0800 writes:

    > Thanks Martin. My hang-up was not on what the outcome of as.complex(NA)
    > should be, but rather, how I should read code like c(x, y) generally. Till
    > now, I have thought of it like 'c(x, y)' is c(as(x, typeof(y)), y)` when
    > "type(y) > type(x)". Basically in my mind, "coercion" in R <->
    > as.<newtype>(.) (or coerceVector() in C).

    > So I tracked down the source (which admittedly has been this way for much
    > longer than the present discussion) to see what exactly c() is doing in
    > this case:

    > https://github.com/r-devel/r-svn/blob/71e7480b07767f3b7d5c45a4247959aa4d83d910/src/main/bind.c#L418-L425

    > And indeed! It's not "coercion" in the sense I just described... there's a
    > branch for the 'x == NA_LOGICAL' case to _convert_ to NA_complex_.

Yes; "of course" ... still, I did not answer your main question,
as you did ask +/-  if  c() should not get an adjustment to the
new  as.complex(<numeric-alike>)  |-->  (Re = NA, Im = 0)
behavior.

And that is still a valid open question. ... contrary to what I
wrote yesterday; sorry for that "answering a different
question".

Martin


    > On Mon, Nov 6, 2023 at 3:08 AM Martin Maechler <maechler using stat.math.ethz.ch>
    > wrote:

    >> >>>>> Michael Chirico
    >> >>>>>     on Sun, 5 Nov 2023 09:41:42 -0800 writes:
    >> 
    >> > This is another follow-up to the thread from September
    >> > "Recent changes to as.complex(NA_real_)".
    >> 
    >> > A test in data.table was broken by the changes for NA
    >> > coercion to complex; the breakage essentially comes from
    >> 
    >> > c(NA, 0+1i)
    >> > # vs
    >> > c(as.complex(NA), 0+1i)
    >> 
    >> > The former is the output we tested against; the latter is
    >> essentially (via
    >> > coerceVector() in C) what's generated by our data.table::shift()
    >> 
    >> > However, these are now (r85472) different:
    >> 
    >> > Im(c(NA, 0+1i))
    >> > # [1] NA  1
    >> > Im(c(as.complex(NA), 0+1i))
    >> > # [1] 0 1
    >> 
    >> 
    >> > The former matches the behavior of directly using NA_complex_:
    >> 
    >> > Im(c(NA_complex_, 0+1i))
    >> > # [1] NA  1
    >> 
    >> > On R4.3.2, they both match the NA_complex_ behavior:
    >> > Im(c(NA, 0+1i))
    >> > # [1] NA  1
    >> > Im(c(as.complex(NA), 0+1i))
    >> > # [1] NA 1
    >> 
    >> > Is this intended behavior, does something need to be updated for c()
    >> as
    >> > well?
    >> 
    >> > Certainly it's messing with my understanding of how c() behaves,
    >> e.g. in ?c
    >> 
    >> >> All arguments are coerced to a common type which is the type of the
    >> > returned value
    >> 
    >> I think you have confused yourself, and everything behaves as expected:
    >> 
    >> As we now have (in R-devel, since {r85233 | maechler | 2023-09-29 })
    >> 
    >> • ‘as.complex(x)’ now returns ‘complex(real=x, imaginary=0)’
    >> for _all_ numerical and logical ‘x’, notably also for ‘NA’
    >> or ‘NA_integer_’.
    >> 
    >> ==> as.complex(NA) is indeed  complex(real = NA, imaginary = 0)
    >> 
    >> And now, in your
    >> 
    >> c(as.complex(NA), 0+1i)
    >> 
    >> you are calling c() on two complex numbers, i.e., there is *no* coercion
    >> (and c(.) is rather "trivial"),  and the same is true for
    >> 
    >> c(NA_complex_, 0+1i)
    >> 
    >> 
    >> However, in 85233, I had only modified & added examples to  ?as.complex,
    >> and now have added more (corresponding to the above NEWS entry);
    -> svn rev 85475
    >> 
    >> .............
    >> 
    >> The underlying "dilemma" that nobody can help us with is that
    >> "almost infinitely" many different complex numbers z fulfill
    >> is.na(z) |--> TRUE
    >> and only one of them is  NA_complex_  and that may be unintuitive.
    >> 
    >> OTOH, we already have for the doubles that there are at least two
    >> different x fulfulling is.na(x), namely  NaN and NA
    >> and from C's point of view there are even considerably more
    >> different NaN's .. but now I'm definitely digressing.
    >> 
    >> Martin
    >> 

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