[R] read-in, error???

[William Dunlap]

You didn't mention it, but did you use something like
   options(digits=20)
before displaying that data?  In any case,
  >  1000000000000.4000244 == 1000000000000.4
  [1] TRUE
because R uses the IEEE-754 double precision floating point
arithmetic that all modern computers support.  That gives
you 52 binary digits of precision, somewhat less than 17 decimal
digits, so your difference in the 18th digit is ignored.

If you need more than 16 decimal digits of precision, you
could break the numbers into parts (via string manipulation,
before reading them as numbers) and or use a high precision
package like Rmpfr to manipulate them (it will be slow and  has
limited functionality).

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 Istvan Nemeth
> Sent: Friday, May 04, 2012 6:55 AM
> To: r-help at r-project.org
> Subject: [R] read-in, error???
> 
> Dear Users!
> 
> I encountered with some problem in data reading while I challenged R (and
> me too) in a validation point of view.
> In this issue, I tried to utilize some reference datasets (
> http://www.itl.nist.gov/div898/strd/index.html).
> And the result departed a bit from my expectations. This dataset dedicated
> to challenge cancellation and accumulation errors (case SmLs07), that's why
> this uncommon look of txt file.
> 
> Treatment   Response
>            1    1000000000000.4
>            1    1000000000000.3
>            1    1000000000000.5
>            ......
>            2    1000000000000.2
>            2    1000000000000.4
>            .....
>            3    1000000000000.4
>            3    1000000000000.6
>            3    1000000000000.4
>            .........
> then after a read.table() I expect the same set instead I've got this:
> 
>     Treatment              Response
> 1           1 1000000000000.4000244
> 2           1 1000000000000.3000488
> 3           1 1000000000000.5000000
> .........
> 22          2 1000000000000.3000488
> 23          2 1000000000000.1999512
> 24          2 1000000000000.4000244
> .......
> 58          3 1000000000000.4000244
> 59          3 1000000000000.5999756
> 60          3 1000000000000.4000244
> 61          3 1000000000000.5999756
> 62          3 1000000000000.4000244
> ......
> a lots of number from the space. I assume that these numbers come from the
> binary representation of such a tricky decimal numbers but my question is
> how can I avoid this feature of the binary representation?
> 
> Moreover, I wondered that it may raise some question in a regulated
> environment.
> 
> 	[[alternative HTML version deleted]]
> 
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