[Rd] type.convert and doubles

[Gregory R. Warnes]

On Apr 26, 2014, at 4:59 PM, Martin Maechler <maechler at stat.math.ethz.ch> wrote:

> 
>> I think there should be two separate discussions:
> 
>> a) have an option (argument to type.convert and possibly read.table) to enable/disable this behavior. I'm strongly in favor of this.
> 
> In my (not committed) version of R-devel, I now have
> 
>> str(type.convert(format(1/3, digits=17), exact=TRUE)) 
>  Factor w/ 1 level "0.33333333333333331": 1
>> str(type.convert(format(1/3, digits=17), exact=FALSE))
>  num 0.333
> 
> where the 'exact' argument name has been ``imported'' from the
> underlying C code.
> 

Looks good to me!

> <snip>
> 
> Instead of only  TRUE/FALSE, we could consider NA with 
> semantics "FALSE + warning" or also "TRUE + warning”.
> 
> 
>> b) decide what the default for a) will be. I have no strong opinion, I can see arguments in both directions
> 
> I think many have seen the good arguments in both directions.
> I'm still strongly advocating that we value long term stability
> higher here, and revert to more compatibility with the many
> years of previous versions.
> 
> If we'd use a default of 'exact=NA', I'd like it to mean
> FALSE + warning, but would not oppose much to  TRUE + warning.
> 

I vote for the default to be “exact=NA” meaning “FALSE + warning" 

-Greg