[Rd] dput()

[Ben Bolker]

 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.

  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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