From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2008-03-25T21:38:13+09:00
Subject: Re: numbers of a record in an array

On Tue, Mar 25, 2008 at 11:23 AM, Robert Klemme
<shortcutter@googlemail.com> wrote:
> 2008/3/25, Jesús Gabriel y Galán <jgabrielygalan@gmail.com>:
> > On Tue, Mar 25, 2008 at 10:09 AM, Bu Mihai <mihai.bulhac@yahoo.com> wrote:
>  >  > a have an array array=["a","b","c","a","b"]
>  >  >  how can i find the numbers of "a", "b","c" items in the array?
>  >  irb(main):006:0> a = %w{a b a c b a c c}
>  >  => ["a", "b", "a", "c", "b", "a", "c", "c"]
>  >  irb(main):007:0> h = Hash.new {|h,k| h[k] = 0}
>  >  => {}
>  >  irb(main):008:0> a.each {|x| h[x] += 1}
>  >  => ["a", "b", "a", "c", "b", "a", "c", "c"]
>  >  irb(main):009:0> h
>  >  => {"a"=>3, "b"=>2, "c"=>3}
>
>  Here's another
>
>  irb(main):001:0> a = %w{a b a c b a c c}
>
> => ["a", "b", "a", "c", "b", "a", "c", "c"]
>  irb(main):002:0> a.inject(Hash.new(0)){|cnt,e| cnt[e]+=1; cnt}
>
> => {"a"=>3, "b"=>2, "c"=>3}
>
>  Jesús, note that you do not need the block form of Hash.new because of
>  the way + works.  It is sufficient to make 0 the default element.

Oh, that's right. I'm so used to that form for defaulting to an array :-).
You say the reason is because of how + works, but is it not the reason
the fact that 0 is an immediate value
of which there's only one instance? So having the same reference to
the 0 object works, whereas having the same
reference to an array (for example) wouldn't achieve the desired effect?

Thanks,

Jesus.