[R] help for the first poster- a simple question

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 03.03.2008 20:12:34:

> Thanks for all response. Here  is  more closer to my question,
> p<-0.05
> 
> f<-0.05
> 
> ld<-sqrt(f* (1 - f) * p * (1 - p))
> 
> D <- (p * (1 - f) - ld)/p
> 
> d <- ((1 - p) * f - ld)/(1 - p)
> 
> haplo<-data.frame(D,d)
> 
> > haplo
>               D             d
> 1 -1.387779e-16 -7.304099e-18
> 
> cond1<-pmin(haplo[,1],haplo[,2])
> 
> haplo[cond1>=0,]

Either do not use computers as they sometimes can not represent exactly 
fractional values. Or use rounding, 
haplo[round(cond1, 10)>=0,]

Regards
Petr

> 
> But  the  program cannot get  right one, because
> 
> 
>  -1.387779e-16>=0 is FALSE
> 
>  -7.304099e-18>=0 is FALSE
> 
> 
> 
> Thank you!
> 
> xj.
> 
> 
> ----- Original Message ----- 
> From: "Gavin Simpson" <gavin.simpson at ucl.ac.uk>
> To: "Xuejun Qin" <xjq at chg.duhs.duke.edu>
> Cc: <r-help at r-project.org>
> Sent: Monday, March 03, 2008 12:57 PM
> Subject: Re: [R] help for the first poster- a simple question
> 
> 
> > On Mon, 2008-03-03 at 12:52 -0500, Xuejun Qin wrote:
> >> Hi, there,
> >> I cannot  get accurate value  for calculation.
> >> for example:
> >> ld<-
> >> 0.05*0.95-ld=-6.938894e-18
> >> 0.05*0.95-ld==0 is False.
> >>
> >> I met this problem in my program, how can I handle it. Thanks.
> >
> > Answer 1:
> >
> > Read FAQ 7.31 -
> >
> > 
http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-

> numbers-are-equal_003f
> >
> > Answer 2:
> >
> > Use all.equal()
> >
> >> ld<-sqrt(1*0.05*0.95*0.05*0.95)
> >> 0.05*0.95-ld
> > [1] -6.938894e-18
> >> 0.05*0.95-ld==0
> > [1] FALSE
> >> all.equal(0.05*0.95-ld, 0)
> > [1] TRUE
> >
> >>
> >>
> >> xj.
> >
> > HTH
> >
> > G
> > -- 
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> > Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
> > ECRC, UCL Geography,          [f] +44 (0)20 7679 0565
> > Pearson Building,             [e] gavin.simpsonATNOSPAMucl.ac.uk
> > Gower Street, London          [w] http://www.ucl.ac.uk/~ucfagls/
> > UK. WC1E 6BT.                 [w] http://www.freshwaters.org.uk
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> >
> >
> 
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