[R] The end of Matlab

[Claudia Beleites]

> > 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