[Rd] [External] Re: zapsmall(x) for scalar x
Steve Martin
@tevem@rt|n041 @end|ng |rom gm@||@com
Mon Dec 18 13:56:46 CET 2023
Does mFUN() really need to be a function of x and the NA values of x? I
can't think of a case where it would be used on anything but the non-NA
values of x.
I think it would be easier to specify a different mFUN() (and document this
new argument) if the function has one argument and is applied to the non-NA
values of x.
zapsmall <- function(x,
digits = getOption("digits"),
mFUN = function(x) max(abs(x)),
min.d = 0L
) {
if (length(digits) == 0L)
stop("invalid 'digits'")
if (all(ina <- is.na(x)))
return(x)
mx <- mFUN(x[!ina])
round(x, digits = if(mx > 0) max(min.d, digits - as.numeric(log10(mx)))
else digits)
}
Steve
On Mon, Dec 18, 2023, 05:47 Serguei Sokol via R-devel <r-devel using r-project.org>
wrote:
> Le 18/12/2023 à 11:24, Martin Maechler a écrit :
> >>>>>> Serguei Sokol via R-devel
> >>>>>> on Mon, 18 Dec 2023 10:29:02 +0100 writes:
> > > Le 17/12/2023 à 18:26, Barry Rowlingson a écrit :
> > >> I think what's been missed is that zapsmall works relative to
> the absolute
> > >> largest value in the vector. Hence if there's only one
> > >> item in the vector, it is the largest, so its not zapped. The
> function's
> > >> raison d'etre isn't to replace absolutely small values,
> > >> but small values relative to the largest. Hence a vector of
> similar tiny
> > >> values doesn't get zapped.
> > >>
> > >> Maybe the line in the docs:
> > >>
> > >> " (compared with the maximal absolute value)"
> > >>
> > >> needs to read:
> > >>
> > >> " (compared with the maximal absolute value in the vector)"
> >
> > > I agree that this change in the doc would clarify the situation
> but
> > > would not resolve proposed corner cases.
> >
> > > I think that an additional argument 'mx' (absolute max value of
> > > reference) would do. Consider:
> >
> > > zapsmall2 <-
> > > function (x, digits = getOption("digits"), mx=max(abs(x),
> na.rm=TRUE))
> > > {
> > > if (length(digits) == 0L)
> > > stop("invalid 'digits'")
> > > if (all(ina <- is.na(x)))
> > > return(x)
> > > round(x, digits = if (mx > 0) max(0L, digits -
> > > as.numeric(log10(mx))) else digits)
> > > }
> >
> > > then zapsmall2() without explicit 'mx' behaves identically to
> actual
> > > zapsmall() and for a scalar or a vector of identical value, user
> can
> > > manually fix the scale of what should be considered as small:
> >
> > >> zapsmall2(y)
> > > [1] 2.220446e-16
> > >> zapsmall2(y, mx=1)
> > > [1] 0
> > >> zapsmall2(c(y, y), mx=1)
> > > [1] 0 0
> > >> zapsmall2(c(y, NA))
> > > [1] 2.220446e-16 NA
> > >> zapsmall2(c(y, NA), mx=1)
> > > [1] 0 NA
> >
> > > Obviously, the name 'zapsmall2' was chosen just for this
> explanation.
> > > The original name 'zapsmall' could be reused as a full backward
> > > compatibility is preserved.
> >
> > > Best,
> > > Serguei.
> >
> > Thank you, Serguei, Duncan, Barry et al.
> >
> > Generally :
> > Yes, zapsmall was meant and is used for zapping *relatively*
> > small numbers. In the other cases, directly round()ing is
> > what you should use.
> >
> > Specifically to Serguei's proposal of allowing the "max" value
> > to be user specified (in which case it is not really a true
> > max() anymore):
> >
> > I've spent quite a a few hours on this problem in May 2022, to
> > make it even more flexible, e.g. allowing to use a 99%
> > percentile instead of the max(), or allowing to exclude +Inf
> > from the "mx"; but -- compared to your zapsmall2() --
> > to allow reproducible automatic choice :
> >
> >
> > zapsmall <- function(x, digits = getOption("digits"),
> > mFUN = function(x, ina) max(abs(x[!ina])),
> > min.d = 0L)
> > {
> > if (length(digits) == 0L)
> > stop("invalid 'digits'")
> > if (all(ina <- is.na(x)))
> > return(x)
> > mx <- mFUN(x, ina)
> > round(x, digits = if(mx > 0) max(min.d, digits -
> as.numeric(log10(mx))) else digits)
> > }
> >
> > with optional 'min.d' as I had (vaguely remember to have) found
> > at the time that the '0' is also not always "the only correct" choice.
> Do you have a case or two where min.d could be useful?
>
> Serguei.
>
> >
> > Somehow I never got to propose/discuss the above,
> > but it seems a good time to do so now.
> >
> > Martin
> >
> >
> >
> > >> barry
> > >>
> > >>
> > >> On Sun, Dec 17, 2023 at 2:17 PM Duncan Murdoch <
> murdoch.duncan using gmail.com>
> > >> wrote:
> > >>
> > >>> This email originated outside the University. Check before
> clicking links
> > >>> or attachments.
> > >>>
> > >>> I'm really confused. Steve's example wasn't a scalar x, it was
> a
> > >>> vector. Your zapsmall() proposal wouldn't zap it to zero, and
> I don't
> > >>> see why summary() would if it was using your proposal.
> > >>>
> > >>> Duncan Murdoch
> > >>>
> > >>> On 17/12/2023 8:43 a.m., Gregory R. Warnes wrote:
> > >>>> Isn’t that the correct outcome? The user can change the
> number of
> > >>> digits if they want to see small values…
> > >>>>
> > >>>> --
> > >>>> Change your thoughts and you change the world.
> > >>>> --Dr. Norman Vincent Peale
> > >>>>
> > >>>>> On Dec 17, 2023, at 12:11 AM, Steve Martin <
> stevemartin041 using gmail.com>
> > >>> wrote:
> > >>>>> Zapping a vector of small numbers to zero would cause
> problems when
> > >>>>> printing the results of summary(). For example, if
> > >>>>> zapsmall(c(2.220446e-16, ..., 2.220446e-16)) == c(0, ..., 0)
> then
> > >>>>> print(summary(2.220446e-16), digits = 7) would print
> > >>>>> Min. 1st Qu. Median Mean 3rd Qu. Max.
> > >>>>> 0 0 0 0 0 0
> > >>>>>
> > >>>>> The same problem can also appear when printing the results of
> > >>>>> summary.glm() with show.residuals = TRUE if there's little
> dispersion
> > >>>>> in the residuals.
> > >>>>>
> > >>>>> Steve
> > >>>>>
> >>>>>> On Sat, 16 Dec 2023 at 17:34, Gregory Warnes <greg using warnes.net>
> wrote:
> > >>>>>>
> >>>>>> I was quite suprised to discover that applying `zapsmall` to a
> scalar
> > >>> value has no apparent effect. For example:
> > >>>>>>> y <- 2.220446e-16
> > >>>>>>> zapsmall(y,)
> >>>>>> [1] 2.2204e-16
> > >>>>>>
> >>>>>> I was expecting zapsmall(x)` to act like
> > >>>>>>
> > >>>>>>> round(y, digits=getOption('digits'))
> >>>>>> [1] 0
> > >>>>>>
> >>>>>> Looking at the current source code, indicates that `zapsmall` is
> > >>> expecting a vector:
> >>>>>> zapsmall <-
> >>>>>> function (x, digits = getOption("digits"))
> >>>>>> {
> >>>>>> if (length(digits) == 0L)
> >>>>>> stop("invalid 'digits'")
> >>>>>> if (all(ina <- is.na(x)))
> >>>>>> return(x)
> >>>>>> mx <- max(abs(x[!ina]))
> >>>>>> round(x, digits = if (mx > 0) max(0L, digits -
> > >>> as.numeric(log10(mx))) else digits)
> >>>>>> }
> > >>>>>>
> >>>>>> If `x` is a non-zero scalar, zapsmall will never perform rounding.
> > >>>>>>
> >>>>>> The man page simply states:
> >>>>>> zapsmall determines a digits argument dr for calling round(x,
> digits =
> > >>> dr) such that values close to zero (compared with the maximal
> absolute
> > >>> value) are ‘zapped’, i.e., replaced by 0.
> >>>>>> and doesn’t provide any details about how ‘close to zero’ is
> defined.
> > >>>>>>
> >>>>>> Perhaps handling the special when `x` is a scalar (or only contains
> a
> > >>> single non-NA value) would make sense:
> >>>>>> zapsmall <-
> >>>>>> function (x, digits = getOption("digits"))
> >>>>>> {
> >>>>>> if (length(digits) == 0L)
> >>>>>> stop("invalid 'digits'")
> >>>>>> if (all(ina <- is.na(x)))
> >>>>>> return(x)
> >>>>>> mx <- max(abs(x[!ina]))
> >>>>>> round(x, digits = if (mx > 0 && (length(x)-sum(ina))>1 )
> max(0L,
> > >>> digits - as.numeric(log10(mx))) else digits)
> >>>>>> }
> > >>>>>>
> >>>>>> Yielding:
> > >>>>>>
> > >>>>>>> y <- 2.220446e-16
> > >>>>>>> zapsmall(y)
> >>>>>> [1] 0
> > >>>>>>
> >>>>>> Another edge case would be when all of the non-na values are the
> same:
> > >>>>>>
> > >>>>>>> y <- 2.220446e-16
> > >>>>>>> zapsmall(c(y,y))
> >>>>>> [1] 2.220446e-16 2.220446e-16
> > >>>>>>
> >>>>>> Thoughts?
> > >>>>>>
> > >>>>>>
> >>>>>> Gregory R. Warnes, Ph.D.
> >>>>>> greg using warnes.net
> >>>>>> Eternity is a long time, take a friend!
> > >>>>>>
> > >>>>>>
> > >>>>>>
> >>>>>> [[alternative HTML version deleted]]
> > >>>>>>
> >>>>>> ______________________________________________
> >>>>>> R-devel using r-project.org mailing list
> >>>>>> https://stat.ethz.ch/mailman/listinfo/r-devel
> > >>>> [[alternative HTML version deleted]]
> > >>>>
> > >>>> ______________________________________________
> > >>>> R-devel using r-project.org mailing list
> > >>>> https://stat.ethz.ch/mailman/listinfo/r-devel
> > >>> ______________________________________________
> > >>> R-devel using r-project.org mailing list
> > >>> https://stat.ethz.ch/mailman/listinfo/r-devel
> > >>>
> > >> [[alternative HTML version deleted]]
> > >>
> > >> ______________________________________________
> > >> R-devel using r-project.org mailing list
> > >> https://stat.ethz.ch/mailman/listinfo/r-devel
> >
> >
> > > --
> > > Serguei Sokol
> > > Ingenieur de recherche INRAE
> >
> > > Cellule Mathématiques
> > > TBI, INSA/INRAE UMR 792, INSA/CNRS UMR 5504
> > > 135 Avenue de Rangueil
> > > 31077 Toulouse Cedex 04
> >
> > > tel: +33 5 61 55 98 49
> > > email: sokol using insa-toulouse.fr
> > >
> https://www.toulouse-biotechnology-institute.fr/en/plateformes-plateaux/cellule-mathematiques/
> >
> > > ______________________________________________
> > > R-devel using r-project.org mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-devel
>
> ______________________________________________
> R-devel using r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
[[alternative HTML version deleted]]
More information about the R-devel
mailing list