[R] Strange Bug in R

[Rolf Turner]

On 06/10/15 21:28, Berend Hasselman wrote:
>
>> On 6 Oct 2015, at 09:24, Neverstop <neverstop at hotmail.it> wrote:
>>
>> Hi all.
>> I don't understand why R works this way:
>>> rm(list=ls())
>>> require(foreign)
>>> dataset <- read.dta("http://www.ats.ucla.edu/stat/data/ologit.dta")
>>> min(dataset$gpa)
>> [1] 1.9
>>> min(dataset$gpa)>=1.90
>> [1] FALSE
>>> min(dataset$gpa)>=1.9
>> [1] FALSE
>>> min(dataset$gpa)>1.89
>> [1] TRUE
>> Shouldn't I get 3 TRUEs?
>> Am I missing something?
>> Thank you.
>>
>>
>
> See R FAQ 7.31  in https://cran.r-project.org/doc/FAQ/R-FAQ.html
> It should provide clarification for your puzzlement.

Not really.  The problem is one of the precision to which a floating 
point number is *printed* rather than one of the way that floating point 
numbers are *calculated*.  Hence it is not an instance of the 
counter-intuitive nature of floating point arithmetic.  I.e. you could 
have numbers a and b that were calculated and stored to *infinite* 
precision, appear to be equal when printed to some default number of 
significant figures, but are not actually equal.

The problems are related and both involve having some understanding of 
floating point numbers, but they are not the same problem.

cheers,

Rolf Turner

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