[R] Bug or just a problem with the computer precision?

[Peter Dalgaard]

jim holtman wrote:
> You are getting round-off problems (I think it is FAQ 7.33).  Use
> characters since thats what the numbers really are. Convert the
> characters and then use substring.  Also sprintf works:
>
>   
>> sprintf("%.2f", A*100)
>>     
> [1] "470990.00"
>   
>> sprintf("%.2f", A)
>>     
> [1] "4709.90"
>   
>
>   
If sprintf works, so does round(A,2) and I suspect there was a reason
not to use that (what is the result for 4709.8967 supposed to be?). 

It might be better to use a small amount of fuzz:

floor(A *100+1e-10)/100

Or, as indicated: If these are really strings, treat them as such:

> A<-"4709.9000"
> substr(A,1,7)
[1] "4709.90"



> On 10/4/07, Renger van Nieuwkoop <renger at ecoplan.ch> wrote:
>   
>> Hi
>>
>> I have the following problem: I have a lot of numbers that identify
>> import goods according to the Harmonised System (8 numbers in two groups
>> with a dot in between). I want to move to the
>> 6 numbers (4 numbers, dot, two numbers). My trick to do this works for
>> all the numbers in the Harmonised Sytem but not for this one:
>>
>> A<-4709.9000
>> (A<-floor(100 * A ) / 100) = 4709.89
>>
>> But this has to be 4709.90
>>
>> If I do this in Excel it works fine...Any idea how to make sure that I
>> get 4709.90 and not 4709.89?
>>
>> Renger
>>
>>
>>
>> _________________________________________________
>>
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>>
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>>
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>>
>>     
>
>
>   


-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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