as.character on OS X tiger

This is just a question of rounding error.  You are computing 11/999, 
which is not exactly representable.  Most computers use IEC60559 
arithmetic, which gives a precision of .Machine$double.eps ~ 2e-16.  So 
you can expect rounding error around 11/999 * .Machine$double.eps ~ 2e-18. 
However, as.character is documented to represent the number to 15 
significant digits.

On all of Linux (i686 and AMD64), Solaris and Windows boxes I get

a <- 11/999
b <- as.numeric(as.character(a))
b

[1] 0.01101101

a - b

[1] 1.040834e-17

as.character(a)

[1] "0.0110110110110110"

as.character(b)

[1] "0.011011011011011"

and these are different representations of different numbers.

So your claim to get different results on `linux' is not one I can 
reproduce.

The fix is not to rely on the fine details of numerical (or character) 
representations of numbers: perhaps convert them back to numbers and use 
all.equal()?

Hi,
When I run this example code on a G5 the last digit is dropped off on a
binary installation of R (R.app), whereas on a linux machine the digit is
not removed.

# Code:
a <- seq(0,1, length=1000)[12]
a

as.character(a)
as.character(as.numeric(as.character(a)))


# Results I get:
a <- seq(0,1, length=1000)[12]

a

[1] 0.01101101

as.character(a)

[1] "0.0110110110110110"

as.character(as.numeric(as.character(a)))

[1] "0.011011011011011"

Can anyone enlighten me on the subtle difference between OS's, its causing
issues for me when I write to list elements with these characters strings
and some occasionally have lost the last "0".

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595