From: Brian Candler <b.candler@...>
Date: 2009-06-29T21:06:22+09:00
Subject: Re: how to make a variable based on array length and member value

Catsquotl wrote:
> I have an array full_array[] of an arbitrary number of transaction 
> objects.
> within the transaction is a Date member..
> 
>  From the array I have created a new array years[].uniq! based on the
> Date.year members
> 
> what id like to do is take the new arrays members and use them as names
> for variables..
> 
> Say the array holds members for 2007, 2008, 2009
> i`d like to iterate through the full_array and map all members from 2008
> in an array.

Sounds like what you want is a Hash, not an Array. Something like:

year_to_members = {}
members.each do |mem|
  y = mem.date.year
  year_to_members[y] ||= []
  year_to_members[y] << mem
end

p year_to_members[2009]
# this prints an array containing elememnts where date.year == 2009

As others will probably point out, this pattern can be simplified a bit. 
But hopefully it's clear enough as a starting point.

The fundamental point is, you don't want to create "names of variables" 
for each year - even though that is technically possible, as others may 
also point out. The right thing to do is to build a Hash, which is an 
object which associates a key (a year number) with a value (an array of 
transaction objects).

HTH,

Brian.
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