Re: PDL-P: Re: Reduce [was: Re: Random items (old p5p issues)]

[Tuomas Lukka]

> > Well, first of all, 
> > 
> >     10:100, 30:200
> > 
> > is not the same: in Perl it comes out as
> > 
> >     10..100, 30..200
> > 
> >     10, 11, ... , 100, 30, 31, .., 200
> > 
> 
> Additionally, generically it would not necessarily have to be a range of
> integers. The range could be specified as floating point if we are
> specifying a slice in physical coordinates.

If someone is going to write the RFC, remember also the third arg: 

        a:b:c

is the sequence

        a, a+c, a+2*c, ... a+n*c

where n is the largest integer such that a+n*c <= b (important that it's
greater than or equal!).

        a:b

is always the same as

        a:b:1

Also, the usual Perl index tricks should work (these should be specified
in the span so that the code interpreting the span can use its knowledge):

        :               # all the things on this dimension: full span
        5:-1            # 5..last
        5:-1:2          # Every second item, up to the last or second last
        -1:7:3          # Start with last item, then fourth last, etc. until 7.

Note that there need to be different contexts: if floats or negative
integers are allowed then -1 cannot stand for the end but it has to stand
for -1.

        Tuomas