R devel - Jul 2003 - round to even digit (PR#3604)

Full_Name: Karl W Broman
Version: 1.7.1
OS: Linux
Submission from: (NULL) (162.129.44.18)


There appears to be a slight problem with round(); for rounding off a 5, 
it should go to the even digit, but there appear to be some cases where
it goes to an odd digit; see below.

Thanks! karl

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> round(c(0.175, 1.175, 2.175, 3.175, 4.175, 5.175, 6.175, 7.175, 8.175,
9.175),
2)
 [1] 0.18 1.18 2.17 3.17 4.17 5.17 6.17 7.17 8.18 9.18
> round(c(1.75, 11.75, 21.75, 31.75, 41.75, 51.75, 61.75, 71.75, 81.75,
91.75),
1)
 [1]  1.8 11.8 21.8 31.8 41.8 51.8 61.8 71.8 81.8 91.8
> 
> version
         _                
platform i686-pc-linux-gnu
arch     i686             
os       linux-gnu        
system   i686, linux-gnu  
status                    
major    1                
minor    7.1              
year     2003             
month    06               
day      16               
language R                
>

On Thu, 31 Jul 2003 kbroman@jhsph.edu wrote:
> Full_Name: Karl W Broman
> Version: 1.7.1
> OS: Linux
> Submission from: (NULL) (162.129.44.18)
>
>
> There appears to be a slight problem with round(); for rounding off a 5,
> it should go to the even digit, but there appear to be some cases where
> it goes to an odd digit; see below.
>
I think this may be a case where the number doesn't actually end in 5, it
just appears to
> round(217.5)
[1] 218
> round(21.75*10)
[1] 218
> round(2.175*100)
[1] 217
> round(0.2175*1000)
[1] 218
since .175 isn't exactly expressible in binary.

	-thomas

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley@u.washington.edu	University of Washington, Seattle