[Rd] R-devel: as.character() for hexmode no longer pads with zeros

[Henrik Bengtsson]

Thanks for confirming and giving details on the rationale (... and
I'll updated R.utils to use format() instead).

Regarding as.character(x)[j] === as.character(x[j]): I agree with this
- is that property of as.character()/subsetting explicitly
stated/documented somewhere?  I wonder if this is a property we should
all strive for for other types of objects?

/Henrik

On Thu, Sep 23, 2021 at 12:46 AM Martin Maechler
<maechler using stat.math.ethz.ch> wrote:
>
> >>>>> Henrik Bengtsson
> >>>>>     on Wed, 22 Sep 2021 20:48:05 -0700 writes:
>
>     > The update in rev 80946
>     > (https://github.com/wch/r-source/commit/d970867722e14811e8ba6b0ba8e0f478ff482f5e)
>     > caused as.character() on hexmode objects to no longer pads with zeros.
>
> Yes -- very much on purpose; by me, after discussing a related issue
> within R-core which showed "how wrong" the previous (current R)
> behavior of the as.character() method is for
> hexmode and octmode objects :
>
> If you look at the whole rev 80946 , you also read NEWS
>
>  * as.character(<obj>) for "hexmode" or "octmode" objects now
>    fulfills the important basic rule
>
>   as.character(x)[j] === as.character(x[j])
>   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> rather than just calling format().
>
> The format() generic (notably for "atomic-alike" objects) should indeed
> return a character vector where each string has the same "width",
> however, the result of  as.character(x) --- at least for all
> "atomic-alike" / "vector-alike" objects --
> for a single x[j] should not be influenced by other elements in x.
>
>
>
>
>     > Before:
>
>     >> x <- structure(as.integer(c(0,8,16,24,32)), class="hexmode")
>     >> x
>     > [1] "00" "08" "10" "18" "20"
>     >> as.character(x)
>     > [1] "00" "08" "10" "18" "20"
>
>     > After:
>
>     >> x <- structure(as.integer(c(0,8,16,24,32)), class="hexmode")
>     >> x
>     > [1] "00" "08" "10" "18" "20"
>     >> as.character(x)
>     > [1] "0"  "8"  "10" "18" "20"
>
>     > Was that intended?
>
> Yes!
> You have to explore your example a bit to notice how "illogical"
> the behavior before was:
>
> > as.character(as.hexmode(0:15))
>  [1] "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "a" "b" "c" "d" "e" "f"
> > as.character(as.hexmode(0:16))
>  [1] "00" "01" "02" "03" "04" "05" "06" "07" "08" "09" "0a" "0b" "0c" "0d" "0e"
> [16] "0f" "10"
>
> > as.character(as.hexmode(16^(0:2)))
> [1] "001" "010" "100"
> > as.character(as.hexmode(16^(0:3)))
> [1] "0001" "0010" "0100" "1000"
> > as.character(as.hexmode(16^(0:4)))
> [1] "00001" "00010" "00100" "01000" "10000"
>
> all breaking the rule in the NEWS  and given above.
>
> If you want format()  you should use format(),
> but as.character() should never have used format() ..
>
> Martin
>
>     > /Henrik
>
>     > PS. This breaks R.utils::intToHex()
>     > [https://cran.r-project.org/web/checks/check_results_R.utils.html]
>