[R] Unexpected R Behavior: Adding 4 to Large Numbers/IDs Containing Current Year

[David Winsemius]

On Jun 29, 2011, at 2:29 PM, Christopher T. Moore wrote:

> Hello,
>
> I have encountered some unexpected behavior in R that seems to occur  
> as a result of having the current year embedded in a number:

No. that is not the explanation.

>
>> ########################################
>> #Some large numbers, representing IDs.
>> IDs <- c(41255689815201100, 41255699815201100, 41255709815201100)

41255689815201100  > 2*10^9
[1] TRUE

So you may think you are working with integers but youa re in fact  
working with floating point numbers. See the R-FAQ


-- 
David.
>> #In scientific notation
>> IDs
> [1] 4.125569e+16 4.125570e+16 4.125571e+16
>> #Change penalty.
>> options(scipen = 5)
>> #Why does R add 4?
>> IDs
> [1] 41255689815201104 41255699815201104 41255709815201104
>> #Changing from numeric to character makes no difference.
>> as.character(IDs)
> [1] "41255689815201104" "41255699815201104" "41255709815201104"
>> #What happens if I treat the numbers as characters?
> IDs.character <- c("41255689815201100", "41255699815201100",  
> "41255709815201100")
>> #No change.
>> IDs.character
> [1] "41255689815201100" "41255699815201100" "41255709815201100"
>> #R adds 4 upon converting to numeric.
>> as.numeric(IDs.character)
> [1] 41255689815201104 41255699815201104 41255709815201104
> #Is this problem occurring because the current year is embedded in  
> the number?
>> IDs <- c(41255689815201100, 41255699815201000, 41255709815201200)
>> #R is no longer adding 4 to the numbers without "2011".
>> IDs
> [1] 41255689815201104 41255699815201000 41255709815201200
>> ########################################
>
> Am I doing something wrong? Any insight on how I can avoid the  
> problem of R changing numbers on its own? Are others able to  
> replicate this example? Is this some kind of bug? Am I right that  
> this problem is occurring because the current year is embedded in  
> the number? I discovered this when trying to merge two data sets,  
> one with IDs stored numbers and one with IDs as characters. I have  
> replicated this in Windows XP with R 2.12 and Windows 7 with R 2.13  
> (both 32- and 64-bit versions).
>
> Thanks,
> Chris
>
> -- 
> Christopher T. Moore, M.P.P.
> Doctoral Student
> Quantitative Methods in Education
> University of Minnesota
> 44.9785°N, 93.2396°W
> moor0554 at umn.edu
> http://umn.edu/~moor0554
>
> ______________________________________________
> R-help at 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.

David Winsemius, MD
West Hartford, CT