R devel - Oct 2005 - Critical Bug in type conversions: as.integer, trunc, ... (PR#8255)

Full_Name: Grischa T?dt
Version: 2.1.1
OS: windows XP
Submission from: (NULL) (192.108.25.32)


I have a strange behaviour in R, looks like type conversions are messed up.

To reproduce:

expected:
> typeof(3)
[1] "double"
> as.integer(3)
[1] 3

!!!! strange:
> typeof((0.3/0.1))
[1] "double"
> as.integer((0.3/0.1))
[1] 2

also for trunc:
>trunc(c(5,7))
>c(0.5,0.7)/c(0.1,0.1)
and now watch the amazing!!!!:
>trunc((c(0.5,0.7)/c(0.1,0.1)))



My R-Version:
platform i386-pc-mingw32
arch     i386           
os       mingw32        
system   i386, mingw32  
status                  
major    2              
minor    1.1            
year     2005           
month    06             
day      20             
language R

On 10/27/2005 9:24 AM, g.toedt at dkfz.de wrote:
> Full_Name: Grischa T?dt
> Version: 2.1.1
> OS: windows XP
> Submission from: (NULL) (192.108.25.32)
> 
> 
> I have a strange behaviour in R, looks like type conversions are messed up.
This is not a bug, it's normal behaviour for floating point values, 
discussed in the FAQ item on "7.31 Why doesn't R think these numbers
are
equal?"

Duncan Murdoch
> 
> To reproduce:
> 
> expected:
>> typeof(3)
> [1] "double"
> 
>> as.integer(3)
> [1] 3
> 
> !!!! strange:
>> typeof((0.3/0.1))
> [1] "double"
> 
>> as.integer((0.3/0.1))
> [1] 2
> 
> also for trunc:
>>trunc(c(5,7))
>>c(0.5,0.7)/c(0.1,0.1)
> 
> and now watch the amazing!!!!:
>>trunc((c(0.5,0.7)/c(0.1,0.1)))
> 
> 
> 
> 
> My R-Version:
> platform i386-pc-mingw32
> arch     i386           
> os       mingw32        
> system   i386, mingw32  
> status                  
> major    2              
> minor    1.1            
> year     2005           
> month    06             
> day      20             
> language R
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

On Thu, 2005-10-27 at 15:24 +0200, g.toedt at dkfz.de
wrote:
> Full_Name: Grischa T?dt
> Version: 2.1.1
> OS: windows XP
> Submission from: (NULL) (192.108.25.32)
> 
> 
> I have a strange behaviour in R, looks like type conversions are messed up.
> 
> To reproduce:
> 
> expected:
> > typeof(3)
> [1] "double"
> 
> > as.integer(3)
> [1] 3
> 
> !!!! strange:
> > typeof((0.3/0.1))
> [1] "double"
> > as.integer((0.3/0.1))
> [1] 2
> 
> also for trunc:
> >trunc(c(5,7))
> >c(0.5,0.7)/c(0.1,0.1)
> 
> and now watch the amazing!!!!:
> >trunc((c(0.5,0.7)/c(0.1,0.1)))
> trunc((c(0.5,0.7)/c(0.1,0.1)))
[1] 5 6


You are getting bitten (you know where) by floating point representation
issues here:
> print(0.3 / 0.1, digits = 20)
[1] 2.9999999999999995559
> print(0.7 / 0.1, digits = 20)
[1] 6.9999999999999991118

So as.integer() and trunc() is working as intended, since in both cases,
they truncate towards 0.


Bottom line:

NOTABUG


Read R FAQ 7.31 and the reference cited there for more information.

HTH,

Marc Schwartz