From: Andrew Timberlake <andrew@...>
Date: 2009-04-29T15:13:31+09:00
Subject: Re: Hash#map

On Wed, Apr 29, 2009 at 8:00 AM, Fredrik <fredjoha@gmail.com> wrote:
> Is there any good reason why Hash#map does not give back a Hash (Ruby
> 1.8 but same in 1.9 as far as I know)? I often find myself writing
> these kind of things:
>
> newhash = oldhash.inject({}) { |h,(k,v)| h[k] = some_operation(v); h }
>
> but that doesn't look pretty at all in my opinion. I want to just
> write like this:
>
> newhash = oldhash.map { |k,v| some_operation(v) }
>
> I finally got around to change this behaviour for my own code, but are
> all Ruby users supposed to invent this wheel on their own? Wouldn't it
> be better if Hash#map behaved like this? Or is there something I am
> missing?
>
> class Hash
>  def hashmap
>    self.inject({}) do |newhash, (k,v)|
>      newhash[k] = yield(k, v)
>      newhash
>    end
>  end
> end
>
>
> Regards,
> Fredrik
>

Becuase #map comes from form Enumerable (and is an alias for collect)

enum.collect {| obj | block } => array
enum.map {| obj | block } => array

Returns a new array with the results of running block once for every
element in enum.

   (1..4).collect {|i| i*i }   #=> [1, 4, 9, 16]
   (1..4).collect { "cat"  }   #=> ["cat", "cat", "cat", "cat"]


Andrew Timberlake
http://ramblingsonrails.com
http://www.linkedin.com/in/andrewtimberlake

"I have never let my schooling interfere with my education" - Mark Twain