[R] Strange behaviour of as.integer()

[William Dunlap]

Use round(), floor(), or ceiling() to convert
numbers with possible fractional parts to numbers
without fraction parts.

as.integer()'s main use is to convert from one
internal representation (i.e., bit pattern)
of a number to another so you can interface to
C or Fortran code.

Note that as.integer(x) also doesn't "work" when
abs(x)>2^31, while round(), floor(), and ceiling()
do work up to c. 2^52.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Ulrich Keller
> Sent: Thursday, January 07, 2010 4:32 AM
> To: r-help at r-project.org
> Subject: [R] Strange behaviour of as.integer()
> 
> I have encountered a strange behaviour of as.integer() which does not
> seem correct to me. Sorry if this is just an indication of me not
> understanding floating point arithmetic.
> 
> > .57 * 100
> [1] 57
> > .29 * 100
> [1] 29
> 
> So far, so good. But:
> 
> > as.integer(.57 * 100)
> [1] 56
> > as.integer(.29 * 100)
> [1] 28
> 
> Then again:
> 
> > all.equal(.57 * 100, as.integer(57))
> [1] TRUE
> > all.equal(.29 * 100, as.integer(29))
> [1] TRUE
> 
> This behaviour is the same in R 2.10.1 (Ubuntu and Windows) and 2.9.2
> (Windows),
> all 32 bit versions. Is this really intended?
> 
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