Associative arrays (or hash) php to ruby

Question

I'm relatively new to ruby and i came from php. One thing that it seems i would not understand is the difference between hashes and arrays. How do you implement associative arrays in ruby? Eg.

$albums = array();
$songs = array();
$songs[] = array('title' => 'Title 1', 'artist' => 'Artist 1', 'album' => 'Album 1');
$songs[] = array('title' => 'Title 2', 'artist' => 'Artist 2', 'album' => 'Album 2');
$songs[] = array('title' => 'Title 3', 'artist' => 'Artist 1', 'album' => 'Album 1');
$songs[] = array('title' => 'Title 4', 'artist' => 'Artist 1', 'album' => 'Album 1');
$songs[] = array('title' => 'Title 5', 'artist' => 'Artist 3', 'album' => 'Album 1');
foreach($songs as $song)
{
  if( !isset($albums[$song['album']]) ) $albums[$song['album']] = array();
  $albums[$song['album']]['title'] = $song['album'];
  $albums[$song['album']]['songs'] = $song;
}
print_r($albums);
['Album 1']
  => 'title' => 'Album 1'
  => 'songs'
    => 'title' => 'Title 1', 'artist' => 'Artist 1', 'album' => 'Album 1'
    => 'title' => 'Title 3', 'artist' => 'Artist 1', 'album' => 'Album 1'
    => 'title' => 'Title 4', 'artist' => 'Artist 1', 'album' => 'Album 1'
    => 'title' => 'Title 5', 'artist' => 'Artist 3', 'album' => 'Album 1'
['Album 2']
  => 'title' => 'Album 2'
  => 'songs'
    => 'title' => 'Title 1', 'artist' => 'Artist 1', 'album' => 'Album 1'

Or even, instead of title and songs i can declare an array album info with title, artist and how many songs.

How can i do something similar with ruby? what i would use to accomplish that?

Answer 1

A more-or-less direct rewrite from your PHP:

albums = {}
songs = [
  { :title => 'Title 1', :artist => 'Artist 1', :album => 'Album 1' },
  { :title => 'Title 2', :artist => 'Artist 2', :album => 'Album 2' },
  { :title => 'Title 3', :artist => 'Artist 1', :album => 'Album 1' },
  { :title => 'Title 4', :artist => 'Artist 2', :album => 'Album 1' },
  { :title => 'Title 5', :artist => 'Artist 3', :album => 'Album 1' }
]
songs.each do |song|
  album = albums[song[:album]] ||= {}
  album[:title] = song[:title]
  (album[:songs] ||= []).push(song)
end
puts albums.inspect

Easier would be the one-liner:

albums = songs.group_by { |song| song[:album] }

Arrays have only integer keys, and allocate all of them up to the highest one (so if you assign foo[100] = 1 , there will be locations for keys 0-99 also occupying memory (with nil value); you note array values with square brackets: [1, 2, 3] is a 3-element array, [] is empty.

Hashes are enclosed in curly braces {} , and can have pretty much anything as keys. However, blocks can also be written with braces, so take care not to confuse the two.

Answer 2

您应该能够像使用PHP关联数组一样使用Ruby Hash。

Answer 3

As you mentioned in the title of your question, associative arrays are usually referred to as hashes in Ruby. The syntax is slightly different from arrays.

# Normal array
normArray = ["SomeSong", "SomeGuy"]
anotherNormArray = Array.new

# Literal hash
literalHash = { "Title" => "SomeSong", "Artist" => "SomeGuy" }

# Declared beforehand
declaredHash = Hash.new
declaredHash["Songs"] = literalHash

Answer 4

You can do it in one line

songs = [
  {'title' => 'Title 1', 'artist' => 'Artist 1', 'album' => 'Album 1'},
  {'title' => 'Title 2', 'artist' => 'Artist 2', 'album' => 'Album 2'},
  {'title' => 'Title 3', 'artist' => 'Artist 1', 'album' => 'Album 1'},
  {'title' => 'Title 4', 'artist' => 'Artist 1', 'album' => 'Album 1'},
  {'title' => 'Title 5', 'artist' => 'Artist 3', 'album' => 'Album 1'}
]
songs.group_by{|h| h[:album]}.inject({}){|h,(album,s)| h[album] = {:title => album, :songs => s }; h }
#=> {"Album 1"=>{:songs=>[{:artist=>"Artist 1", :album=>"Album 1", :title=>"Title 1"}, {:artist=>"Artist 1", :album=>"Album 1", :title=>"Title 3"}, {:artist=>"Artist 2", :album=>"Album 1", :title=>"Title 4"}, {:artist=>"Artist 3", :album=>"Album 1", :title=>"Title 5"}], :title=>"Album 1"}, "Album 2"=>{:songs=>[{:artist=>"Artist 2", :album=>"Album 2", :title=>"Title 2"}], :title=>"Album 2"}}

Only I don't understand why do you use Album title twice: as a hash key and as a title param? You should use only once, I think :)