[Rd] R (>= 3.4.0): integer-to-double coercion in comparisons no longer done (a good thing)

[Michael Lawrence]

Thanks for highlighting this. I just made the change one day. Guess I
should have mentioned it in the NEWS.

Michael

On Sat, Jan 27, 2018 at 3:01 PM, Henrik Bengtsson <
henrik.bengtsson at gmail.com> wrote:

> Hi,
>
> there was a memory improvement done in R going from R 3.3.3 to R 3.4.0
> when it comes to comparing an integer 'x' an double 'y' (either may be
> scalar or vector).
>
> For example, in R 3.3.3, I get:
>
> > getRversion()
> [1] '3.3.3'
> > x <- integer(1000)
> > y <- double(1000)
> > profmem::profmem(z <- (x < y))
> Rprofmem memory profiling of:
> z <- (x < y)
>
> Memory allocations:
>       bytes      calls
> 1      8040 <internal>
> 2      4040 <internal>
> total 12080
> >
>
> and in R 3.4.0, I get:
>
> > getRversion()
> [1] '3.4.0'
> > x <- integer(1000)
> > y <- double(1000)
> > profmem::profmem(z <- (x < y))
> Rprofmem memory profiling of:
> z <- (x < y)
>
> Memory allocations:
>       bytes      calls
> 1      4040 <internal>
> total  4040
>
> Note how in R (<= 3.3.3), the (x < y) comparison will cause an
> internal coercion of integer vector 'x' into a double, which then can
> be compared to double 'y'.  In R (>= 3.4.0), it appears that this
> coercion is done per element and will therefore avoid introducing a
> new, temporary copy internally.  The same is observed with when
> comparing with (x == y).
>
> This is a great improvement that I think deserves more credit.  I
> couldn't find any mentioning of it in the R 3.4.0 NEWS
> (https://cran.r-project.org/doc/manuals/r-release/NEWS.html).  Does
> anyone know whether this was a specific improvement for such
> comparison, or a side effect of something else, e.g. an improved byte
> compiler?
>
> Thanks,
>
> Henrik
>
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