From: Tom Reilly <w3gat@...>
Date: 2011-04-13T10:52:40+09:00
Subject: Re: hash of arrays

Define hash of hashes this way

#Using a default hash.

foo = Hash.new { |hash, key| hash[key] = Hash.new }

foo["a"][1] = "one"
foo["a"][2] = "a two"
foo["b"][3] = "b three"
foo["a"][4] = "b four"

p foo["a"][1]
p foo["a"][4]
p foo["a"].size
foo["a"].each {|x,y| p "#{x}  #{y}"}

David Sprague wrote:
> 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.
>
> 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
>
> or the ternary equivalent in the inner loop?
>
> thanks,
>
> Dave
>
>