[R] strange digit switching

[Peter Dalgaard]

Hans-Peter <gchappi at gmail.com> writes:

> Hi,
> 
> I execute the following code snippet.What I don't understand is, that in the
> first two cases the numbers shown don't correnspondant to the input (though
> I have set the options to show 22 digits). When I assign the third number
> which has one place, the display of the numbers is suddenly correct.
> 
> Can anybody explain what happens here?
> (this is just a sample, my real problem lies in numbers that I import from a
> datafile and I don't know how to control them when this switching occurs)

This looks like it is windows specific: digits=22 is interpreted as 17
or so. On Linux (FC5) I see a few more digits, but I still get an
extra decimal in the 3rd case. 

This is natural since 0.19... needs one more decimal place to be
represented to N digit accuracy than does 6.94... and 8.34...
 
> ###########################
> options( digits=22 )
> x <- matrix(NA, 3,1)
> x[1] <- 6.94788635771657950
> x      # 6.947886357716580     # DIFFERENT ???
>         # NA
>         # NA
> x[1] == 6.94788635771657950   # but is the same
> 
> x[2] <- 8.34284937565404050
> x      # 6.947886357716580     # DIFFERENT ???
>         # 8.342849375654041     # DIFFERENT ???
>         # NA
> x[1] == 6.94788635771657950   # but is the same
> 
> x[3] <- 0.19043842368566377
> x      # 6.94788635771657950   # NOW OK!!!
>         # 8.34284937565404050   # "   "
>         # 0.19043842368566377   # "   "
> x[1] == 6.94788635771657950   # but is the same
> 
> 
> ###
> platform       i386-pc-mingw32
> arch           i386
> os             mingw32
> system         i386, mingw32
> status
> major          2
> minor          3.1
> year           2006
> month          06
> day            01
> svn rev        38247
> language       R
> version.string Version 2.3.1 (2006-06-01)
> 
> 
> -- 
> Regards,
> Hans-Peter
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907