From: Olivier Renaud <o.renaud@...>
Date: 2007-09-23T03:05:46+09:00
Subject: Re: Idiomatic Ruby for Array#extract / Range#length?

Le jeudi 20 septembre 2007 14:28, Sammy Larbi a �crit�:
> During the monthly meeting of our code dojo, we were surprised by a couple
> of things in Ruby, so I had a couple of questions I'd like to ask the
> community:
>
> 1) Would it make sense to talk about a Range having a length, as in:
>
> class Range
>       def length
>            self.end - self.begin
>       end
> end

This code will work only when begin and end respond to #-. This is a valid 
implementation for Numeric objects, but not for other classes.
In the general case, you'd have to generate every objects of the range to 
count them (using #to_a and #size).
And as the previous posts were debating, some ranges are not able to generate 
the objects in the Range : the ranges of objects that do not respond to 
#succ. And some ranges can be infinite.
By the way, generating all objects and counting is not restricted to Range, 
but is general for any other Enumerable.

>
> 2) What about a 2 dimensional slice (you want a submatrix, for example)?
>
> def test_extract_submatrix
>   assert_equal [[1,2,3],[4,5,6],[7,8,9]].extract_submatrix(1..2,1..2)
> , [[5,6],[8,9]]
> end
>
> class Array
>   def extract_submatrix(row_range, col_range)
>     self[row_range].transpose[col_range].transpose
>   end
> end

Yes, this may be a useful method. It could be extended for use with 
n-dimensional arrays.
Take a look to NArray library. I'm not sure, but I think it can do what you 
are looking for, in an optimized way.

> 3)  Are the better/more idiomatic ways to do these?

Your code is fine :)

> 4) Excuse my ignorance, as I've yet to use Facets, but are these the type
> of things it adds (and more)?  Are they already in there?

Yes, the submatrix thing is the kind of method I could expect to see in 
Facets. I'm not aware of the existence of such a method, though.

> Thanks and kind regards,
> Sam

-- 
Olivier Renaud