[R] Unexpected result from binary greater than operator

[Sundar Dorai-Raj]

chris.bodily at autolivasp.com wrote:
> Hi All,
> 
> I recently encountered results that I did not expect, exhibited by the
> following code snippet:
> 
> test <- function() {
>     minX <- 4.2
>     min0 <- 4.1
>     sigmaG <- 0.1
>     Diff <- minX-min0
>     print(c(Diff=Diff,sigmaG=sigmaG))
>     cat("is Diff > sigmaG?:", Diff > sigmaG,"\n")
>     cat("is (4.2 - 4.1) > 0.1?:",(4.2 - 4.1) > 0.1,"\n")
>     cat("is 0.1 > 0.1?:", 0.1>0.1,"\n")
> }
> 
> When I execute the above function I get the following:
> 
>>test()
> 
>   Diff sigmaG
>    0.1    0.1
> is Diff > sigmaG?: TRUE
> is (4.2 - 4.1) > 0.1?: TRUE
> is 0.1 > 0.1?: FALSE
> 
> Can someone please help me understand why R returns TRUE for (4.2 - 4.1) >
> 0.1 ?
> 
> Thanks so much,
> Chris
> 
> 
> I'm running the precompiled R-2.2.0 binary for Windows on WinXP Pro SP1.
> 
> 
>>Sys.getlocale()
> 
> "LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
> States.1252;LC_MONETARY=English_United
> States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252"
> 
> 
>>version
> 
>          _
> platform i386-pc-mingw32
> arch     i386
> os       mingw32
> system   i386, mingw32
> status
> major    2
> minor    2.0
> year     2005
> month    10
> day      06
> svn rev  35749
> language R
> 

Seems like this is coming up about once a week. See FAQ 7.31.

http://cran.r-project.org/doc/FAQ/R-FAQ.html

Hint:

print(4.2 - 4.1, digits = 16)

--sundar