[R] sensitivity logical operators in R

[Nordlund, Dan (DSHS/RDA)]

Marc

You have been given the answer already and a solution.  See the R FAQ 7.31.  As you have discovered this issue is not specific to R.  In order to eliminate this "problem" entirely, you will need a computer system with infinite precision. 

Dan

Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Marc Jekel
> Sent: Monday, January 24, 2011 11:48 AM
> Cc: r-help at r-project.org
> Subject: Re: [R] sensitivity logical operators in R
> 
> Hi again,
> 
> I have checked the same code (see below) using MATLAB. It produces the
> same error (i.e., equal numbers are evaluated as unequal). Do I miss
> something?
> 
> Thanks for help!
> 
> Marc
> 
> Marc Jekel schrieb:
> > Hello R Fans,
> >
> > Another question for the community that really frightened me today.
> > The following logical comparison produces a "false" as output:
> >
> > t = sum((c(.7,.69,.68,.67,.66)-.5)*c(1,1,-1,-1,1))
> > tt = sum((c(.7,.69,.68,.67,.66)-.5)*c(1,-1,1,1,-1))
> >
> > t == tt
> >
> > This is really strange behavior. Most likely this has something to do
> > how R represents numbers internally and the possible sensitivity of a
> > computer? Does anyone know when this strange behavior occurs and how
> > to fix it?
> >
> > Thank you all! This list is pleasure!!!
> >
> > Marc
> >
> 
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