"John Porter" wrote:
> Sterin, Ilya wrote:
> > Don't really know which would be more helpful, since I first need to
find a
> > scenerio where I would use this facility, then what result would I
expect
> > once the shortest list runs out.
>
> Let us ask the PDL folks.
>
> In fact, I'm quite sure this has been done already.
>
Well, I'm not a PDL folk, but I'm a p6-data folk so perhaps I qualify.
The interest in non-matching indices comes in 'broadcasting', which,
assuming the element-wise operators mentioned by Larry, works like this:
@b = (1,2,3);
@c = (2,4,6);
@d := @b :* @c; # Returns (2,8,18)
@e := 3 :* @c; # Returns (6,12,18)
Notice that the scalar '3' is 'broadcast' across the length of @c just as if
it was the list (3,3,3).
Or if you prefer text-crunching examples to number crunching, it works like
this:
@people = ('adam', 'eve ', 'bob ');
@scores = (7,9,5); # Score for each person
@histogram := '#' :x @scores; # Returns ('xxxxxxx','xxxxxxxxx','xxxxx')
print join("\n", @people . ' ' . @histogram);
Notice that the scalar '#' has been broadcast across the length of @scores.
For more information, see:
http://dev.perl.org/rfc/82.html#Broadcasting
which explains the more interesting case of multidimensional broadcasting.
Note that this RFC is a little dated now, in that Larry has proposed the
adverb ':' to mean "apply element-wise", so the examples in the RFC really
need a ':' added before all the operators. Other than that nothing should
need to change.
For Pyton's implementation of this concept, see:
http://starship.python.net/~da/numtut/array.html#SEC19
See also implementations in J and APL (which is the best role model), PDL,
functional languages like Haskell, and mathematical languages like
Mathematica.
