From: Roger Braun <roger@...>
Date: 2011-04-13T10:27:54+09:00
Subject: Re: hash of arrays

Hi David

2011/4/13 David Sprague <david.sprague@gmail.com>:
> I'm wrote this code to bin a list of words by word-length:
>
> dict = Hash.new([])
>
> dict_file.each do |line|
>  line.chomp!()
>  dict[line.length] << line
> end
>
> expecting that I could avoid testing each time whether this was a new
> entry in the hash or not by just appending to the default, an empty
> array,
> if it is new.

See http://ruby-doc.org/core/classes/Hash.html#M000718.

>
> What happens is that the *same* array is assigned as the default value
> to all new entries so that all the hash entries finish with the same
> array of values.
>
> is there away to void having to write something like:
>
> if dict.key?(line.length)
>  dict[line.length] << line
> else
>  dict[line.length] = line
> end

dict = Hash.new{Array.new} should work.

-- 
Roger Braun
rbraun.net | humoralpathologie.de