R devel - May 2007 - round(#, digits=x) unreliable for x=2 (PR#9682)

Full_Name: Scott Wilkinson
Version: 2.3.1
OS: WinXP Pro
Submission from: (NULL) (140.253.203.4)


In the example below round() does not report to the specified number of digits
when the last digit to be reported is zero: Compare behaviour for 0.897575 and
0.946251. Ditto for signif(). The number of sigfigs is ambiguous unless the
reader knows this behaviour. Is this a bug or intended behaviour? Is there a
work-around?

#Example code:
number <- 0.897575 # this one isn't reported to 2 decimal places 0.90 as
expected
#number <- 0.946251 # when the last reported digit is non-zero it gives
expected
behaviour
Round3 <- round(number, digits=3)
Round2 <- round(number, digits=2)       #why 0.9 and not 0.90 for 0.897575?
Round1 <- round(number, digits=1)

Signif3 <- signif(number, digits=3)
Signif2 <- signif(number, digits=2)    #why 0.9 and not 0.90 0.897575?
Signif1 <- signif(number, digits=1)

Results <- data.frame(Round3, Round2, Round1, Signif3, Signif2, Signif1)

On 13/05/2007 8:46 PM, scott.wilkinson at csiro.au
wrote:
> Full_Name: Scott Wilkinson
> Version: 2.3.1
> OS: WinXP Pro
> Submission from: (NULL) (140.253.203.4)
> 
> 
> In the example below round() does not report to the specified number of
digits
> when the last digit to be reported is zero: Compare behaviour for 0.897575
and
> 0.946251. Ditto for signif(). The number of sigfigs is ambiguous unless the
> reader knows this behaviour. Is this a bug or intended behaviour? Is there
a
> work-around?
It's not a bug.  It has nothing to do with round(), it is the way R 
prints numbers by default.  If you ask to print 0.90, you'll get

[1] 0.9

because 0.9 and 0.90 are the same number.  If you want trailing zeros to 
print, you need to specify a format to do that, e.g.

 > noquote(format(0.9, nsmall=2))
[1] 0.90

The noquote stops the "" from printing.  You could also use sprintf()
or
formatC() for more C-like format specifications.

Duncan Murdoch