Thanks a lot for your explanation!

I see the point and I think I'll solve my question using a different method!

Andreia Leite

On Sun, Jun 24, 2012 at 10:53 PM, Oliver Ruebenacker <curoli@gmail.com>wrote:

>     Hello,
>
>  The FAQ answer 7.31 may be confusing to noobs and the referenced
> paper is long. The essence is:
>
>  (1) It's not an R issue, it is a floating point (flop) arithmetic issue.
>  (2) The issue is that flop arithmetic is almost always only approximate.
>  (3) Therefore, asking for exact equality of two flops is almost
> always a mistake.
>  (4) In simple cases, you can take the difference of two flops and
> ask whether it is good enough
>  (5) For extended calculations, you need to keep in mind that errors
> propagate and accumulate.
>  (6) Some ill-defined problems may lead to "solutions" that aren't
> solutions (e.g. trying to invert a singular matrix)
>  (7) Some well-defined problems may defy a straight-forward approach
> (e.g. solving stiff differential equations)
>
>     Take care
>     Oliver
>
> On Sun, Jun 24, 2012 at 5:29 PM, Sarah Goslee <sarah.goslee@gmail.com>
> wrote:
> > Please read R FAQ 7.31, Why doesn't R think these numbers are equal?
> >
> > Sarah
> >
> > On Sun, Jun 24, 2012 at 1:58 PM, Andreia Leite
> > <andreiaheitorleite@gmail.com> wrote:
> >> Dear list,
> >>
> >> I'm trying to do a loop where I should choose a cell of a data frame
> >> comparing it with another. The code actually works for the majority of
> the
> >> loop but for some reason it doesn't and I can't figure out why.
> >>
> >> When I tried to understand why I've noticed this:
> >>
> >>> dif[11]
> >> [1] 118.8333
> >>> linhasUpdate[10,6]
> >> [1] 118.8333
> >>> dif[11]==linhasUpdate[10,6]
> >> [1] FALSE
> >>
> >> Even though the values are the same R says they aren't! This happens for
> >> some of the values (44) and for the others (128) it works fine.
> >>
> >> Does anybody why is this happening or a way to fix it? I' using 2.15.0.
> >>
> >> Thanks a lot!
> >>
> >> Andreia Leite
> >>
> >> --
> > --
> > Sarah Goslee
> > http://www.functionaldiversity.org
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Oliver Ruebenacker, Bioinformatics and Network Analysis Consultant
> President and Founder of Knowomics
> (http://www.knowomics.com/wiki/Oliver_Ruebenacker)
> Consultant at Predictive Medicine
> (http://predmed.com/people/oliverruebenacker.html)
> SBPAX: Turning Bio Knowledge into Math Models (http://www.sbpax.org)
>



-- 
Andreia Leite

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