[R] "which" is wrong?

[Uwe Ligges]

Troels Ring wrote:

> Dear friends,
> R 2.0.1 on windows XP:
> 
> TOT <-  seq(0.01,1,by=0.01)
>  which(TOT==0.06)
> # numeric(0)
> which(TOT>0.06)
> # [1]   6   7   8  etc
> which(TOT<0.06)
> #[1] 1 2 3 4 5
>  TOT[6]
> #[1] 0.06
> TOT[6]==0.06
> #[1] FALSE
> 
> but
> TOT[5]==0.05
> #[1] TRUE
>  and
>  which(TOT==0.05)
> # [1] 5
> 
> 
> 
> 
> 
> TOT looks as expected when printed,
> 0.35 and 0.36 behaves similarly
> 
> I have tried on another machine with the same result - wonder what 
> happens and whether
> this is as expected ?


It is expected: the 0.06 *calculated* by seq() is computationally a 
little bit different than the 0.06 you have typed - we are working with 
floating point calculations on a digital computer.
See ?all.equal for help.

Uwe Ligges


> Best wishes
> Troels Ring,
> Aalborg, Denmark
> 
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