[Rd] dput()

[Duncan Murdoch]

On 29/02/2020 4:19 a.m., Ben Bolker wrote:
> 
>   I think Robin knows about FAQ 7.31/floating point (author of
> 'Brobdingnag', among other numerical packages).  I agree that this is
> surprising (to me).
> 
>    To reframe this question: is there way to get an *exact* ASCII
> representation of a numeric value (i.e., guaranteeing the restored value
> is identical() to the original) ?
> 
>   .deparseOpts has
> 
> ‘"digits17"’: Real and finite complex numbers are output using
>            format ‘"%.17g"’ which may give more precision than the
>            default (but the output will depend on the platform and there
>            may be loss of precision when read back).
> 
>    ... but this still doesn't guarantee that all precision is kept.

"Using control = c("all", "hexNumeric") comes closest to making 
deparse() an inverse of parse(), as representing double and complex 
numbers as decimals may well not be exact. However, not all objects are 
deparse-able even with this option. A warning will be issued if the 
function recognizes that it is being asked to do the impossible."

> 
>    Maybe
> 
>   saveRDS(x,textConnection("out","w"),ascii=TRUE)
> identical(x,as.numeric(out[length(out)]))   ## TRUE
> 
> ?
> 
> 
> 
> 
> On 2020-02-29 2:42 a.m., Rui Barradas wrote:
>> Hello,
>>
>> FAQ 7.31
>>
>> See also this StackOverflow post:
>>
>> https://stackoverflow.com/questions/9508518/why-are-these-numbers-not-equal
>>
>> Hope this helps,
>>
>> Rui Barradas
>>
>> Às 00:08 de 29/02/20, robin hankin escreveu:
>>> My interpretation of dput.Rd is that dput() gives an exact ASCII form
>>> of the internal representation of an R object.  But:
>>>
>>>    rhankin using cuttlefish:~ $ R --version
>>> R version 3.6.2 (2019-12-12) -- "Dark and Stormy Night"
>>> Copyright (C) 2019 The R Foundation for Statistical Computing
>>> Platform: x86_64-pc-linux-gnu (64-bit)
>>>
>>> [snip]
>>>
>>> rhankin using cuttlefish:~ $ R --vanilla --quiet
>>>> x <- sum(dbinom(0:20,20,0.35))
>>>> dput(x)
>>> 1
>>>> x-1
>>> [1] -4.440892e-16
>>>>
>>>> x==1
>>> [1] FALSE
>>>>
>>>
>>> So, dput(x) gives 1, but x is not equal to 1.  Can anyone advise?
>>>
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>>
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