[R] The end of Matlab
Claudia Beleites
cbeleites at units.it
Fri Dec 12 16:21:51 CET 2008
> > Wacek:
> >> x[3:]
> >> instead of
> >> x[3:length(x)]
> >> x[3:end]
> >
> > I don't think that would help:
> > what to use for end - 3 within the convention that negative values mean
> > exclusion?
>
> might seem tricky, but not impossible:
>
> x[-2]
> # could mean 'all except for 2nd', as it is now
>
> x[1:-2]
> # could mean 'from start to the 2nd backwards from the end'
I know you get thus far. You might even think to decide whether exclusion or
'from the end' is meant from ascending ./. descending order of the sequence,
but this messes around with returning the reverse order.
> since r disallows mixing positive and negative indexing, the above would
> not be ambiguous. worse with
>
> x[-3:-1]
>
> which could mean both 'except for 3rd, 2nd, and 1st' and 'from the 3rd
> to the 1st from the end', and so would be ambiguous. in this context,
> indeed, having explicit 'end' could help avoid the ambiguity.
that's the problem.
also: how would 'except from the 5th last to the 3rd last' be expressed?
You won't get 2 independent things into one sign without trouble.
Claudia
--
Claudia Beleites
Dipartimento dei Materiali e delle Risorse Naturali
Università degli Studi di Trieste
Via Alfonso Valerio 6/a
I-34127 Trieste
phone: +39 (0 40) 5 58-34 47
email: cbeleites at units.it
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