From: Kaye Ng <sbstn26@...>
Date: 2010-07-12T17:16:12+09:00
Subject: hash example

Hello. First of all, I'm reading this ebook,
http://www.ruby-doc.org/docs/ProgrammingRuby/
is it a good book?

---------------------------------------------------------------------------------
instSection['oboe']  損  "woodwind"
instSection['cello']  損  "string"
instSection['bassoon']  損  nil

As the last example shows, a hash by default returns nil when indexed by
a key it doesn't contain. Normally this is convenient, as nil means
false when used in conditional expressions. Sometimes you'll want to
change this default. For example, if you're using a hash to count the
number of times each key occurs, it's convenient to have the default
value be zero. This is easily done by specifying a default value when
you create a new, empty hash.

histogram = Hash.new(0)
histogram['key1']  損  0
histogram['key1'] = histogram['key1'] + 1
histogram['key1']  損  1

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I don't understand the histogram example (starting from "For example, if
you're using a hash to count the...") What does Hash.new(0) do and what
is it used for?

A practical and simple example would be great.  Thank you Ruby experts!
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