[Rd] zapsmall(x) for scalar x

[Gregory R. Warnes]

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


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> 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!
>> 
>> 
>> 
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>> 
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