R help - Dec 2009 - what don't I get about numeric/double comparisons in R way?

Hi,

I'm pretty much an R noob and I'm missing some paradigm in R I think.   
I can't figure our how to compare numerics.  here's a transcript of my  
tests.  Any pointers?

 > print(range_sd)
[1] 34.40783

 > is.numeric(range_sd)
[1] TRUE
 > is.numeric(foo)
[1] TRUE
 > is.double(range_sd)
[1] TRUE
 > is.double(foo)
[1] TRUE
 >

 > identical(range_sd, foo)
[1] FALSE

 > identical(range_sd, 34.40783)
[1] FALSE

 > identical(range_sd, 34.40783, num.eq=FALSE)
[1] FALSE

 > identical(range_sd, 34.40783, num.eq=TRUE)
[1] FALSE

 > library(RUnit)
Warning message:
package 'RUnit' was built under R version 2.10.1

 > checkEquals(range_sd, 34.40783)
Error in checkEquals(range_sd, 34.40783) :
   Mean relative difference: 5.79431e-08

 > checkEquals(range_sd, foo)
Error in checkEquals(range_sd, foo) :
   Mean relative difference: 5.79431e-08

 > if( range_sd == 34.40783 ) { print("foo")}
 > if( range_sd == "34.40783" ) { print("foo")}
 > if( range_sd != "34.40783" ) { print("foo")}
[1] "foo"

 > all.equal(range_sd, 34.40783)
[1] "Mean relative difference: 5.79431e-08"

On 12/31/2009 02:41 PM, donahchoo at me.com wrote:
> Hi,
>
> I'm pretty much an R noob and I'm missing some paradigm in R I
think.
> I can't figure our how to compare numerics.  here's a transcript of
my
> tests.  Any pointers?
Hi donahchoo,
You're comparing the printed value of range_sd, which has been 
truncated, to the actual value. As the printout says, the difference is 
small, but present. If you set range_sd to the printed value:

range_sd<-34.40783

the comparisons will return TRUE.

Jim