From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-02-05T00:18:31+09:00
Subject: Re: Hash counting

On Wed, Feb 4, 2009 at 3:27 PM, Martin DeMello <martindemello@gmail.com> wrote:
> On Wed, Feb 4, 2009 at 12:04 AM, Stuart Clarke
> <stuart.clarke1986@gmail.com> wrote:
>>
>>        counts = Hash.new(0)
>>        eventdateID.each {|d| counts[d] += 1}
>
> Here is your problem. Hash.new(0) means "when I query the hash, and
> the key I request is not in there, return 0". It does not actually add
> {key => 0} to the hash itself.

This is true, but counts[d] += 1 is actually counts[d] = counts[d] + 1
so the RHS will evaluate to 1 the first time, assigning it to the hash:

irb(main):001:0> h = Hash.new(0)
=> {}
irb(main):002:0> h["a"] += 1
=> 1
irb(main):003:0> h
=> {"a"=>1}

So the above snippet is correct for generating a histogram.

Jesus.