[Rd] It's a BUG or a Feature? Generating seq break comparing operators

[Davide Rambaldi]

Hello everybody:

I get a strange behavior with seq, take a look at this:

> msd <- seq(0.05,0.3, 0.01)
> msd[13]
[1] 0.17
> class(msd)
[1] "numeric"
> class(msd[13])
[1] "numeric"
> typeof(msd[13])
[1] "double"

now the problem:

> msd[13] == 0.17
[1] FALSE

It is strange only to me?

Consider that:

> 0.17 == 0.17
[1] TRUE

and also

> a <- c(0,1,0.17)
> a
[1] 0.00 1.00 0.17
> a[3] == 0.17
[1] TRUE

It's a BUG in seq? I suspect something related to doubles … 

sessionInfo():

R version 2.15.2 (2012-10-26)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
[1] tools_2.15.2


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Davide Rambaldi, PhD.
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IEO ~ MolMed
[e] davide.rambaldi at ieo.eu
[e] davide.rambaldi at gmail.com