[Rd] [External] Re: zapsmall(x) for scalar x

[Steve Martin]

Sorry for being unclear. I was commenting on the edge case that
Gregory brought up when calling zapsmall() with a vector of small
values. I thought Gregory was asking for thoughts on that as well, but
maybe I misunderstood. IMO it would be weird for zapsmall() to make a
small scalar zero but not a vector of the identical values.

The example with summary() was meant to show that zapping a vector of
small values to 0 could change the current printing behavior for
certain objects. Ducan is right that zapping only a scalar to zero
wouldn't do anything.

>>> Isn’t that the correct outcome?  The user can change the number of digits if they want to see small values…

I'm not sure a user would be able to change the digits without
updating other functions. If xx[finite] <- zapsmall(x[finite]) in
print.summaryDefault() makes a vector of 0s (e.g., zapsmall(x) works
like round(x, digits = getOption("digits")) and getOptions("digits")
is 7) then calling print(summary(2.220446e-16), digits = 16) would
still print a vector of 0s. The digits argument to print() wouldn't do
anything.

In any case, I just wanted to point out that changes to zapsmall() in
the corner case Gregory brought up could affect the way certain
objects are printed, both changing the current behavior and perhaps
requiring changes to some other functions.

Steve

On Sun, 17 Dec 2023 at 12:26, Barry Rowlingson
<b.rowlingson using lancaster.ac.uk> wrote:
>
> 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)"
>
> 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]]
>> >>>
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