[R] what don't I get about numeric/double comparisons in R way?

[donahchoo at me.com]

On Dec 30, 2009, at 10:10 PM, Jim Lemon wrote:

> 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
>

Thanks, Jim.  I figured this out after sending the email, but I still  
can't compare. Here's some more tests, note that all.equal returns  
true but so does !=

actual_mean <- mean( range)
actual_sd <- sd( range)
expected_mean <- 218.213483146067
expected_sd <- 159.277118043936
print(paste("expected_mean", expected_mean))
print(paste("actual_mean", actual_mean))
print(paste("expected_sd", expected_sd))
print(paste("actual_sd", actual_sd))

if( expected_mean != actual_mean ) {
   stop( "not equal" )
}

Output:

 > source("/Users/adhamh/Developer/r/test.r")
[1] "expected_mean 218.213483146067"
[1] "actual_mean 218.213483146067"
[1] "expected_sd 159.277118043936"
[1] "actual_sd 159.277118043936"
Error in eval.with.vis(expr, envir, enclos) : not equal
 > identical(expected_mean, actual_mean)
[1] FALSE
 > all.equal(expected_mean, actual_mean)
[1] TRUE
 >