hash and symbol

hash

arr = [4,1,2,7,"M","A","V"]
arr.partition { |a| a.is_a? String }.map(&:sort).flatten
p arr
=>
["A","V","M",1,2,4,7]
-------
a = [1, "A", nil, "M", "", '']
a.reject!{|a| a.nil? || a.to_s.empty? }
p a
=> 
[1,"A","M"]
-----

Hash
----
   .key, value pairs
   .similar to arrays
create
----
   my_hash = Hash.new
   snd_hash = {}
   trd_hash = Hash.new(0)
 default value
 ------
    trd_hash.default
    => 0
 defining
 ----
 malls = { #with_string
    "forum" => "vadapalani",
    "ea" => "rayapettah",
    "spencer" => "rayapettah"
  }
  
  accesing
  ----
  malls["forum"]
  =>vadapalani
  malls[:forum]
  =>throw a nil
  
  malls.each do |n,l|
    puts "#{n}: #{l}"
  end
  -
  with symbol
  -----
  movies = { 
    ironman: 4.5,
    batman: 5,
    superman: 4.8
  }
  movies[:batman]
  =>
  5
  
  keys
  ----
  movies.keys
  =>
  all keys
  delete
  -----
  movies.delete(:ironman)
  length
  -----
  movies.length
  => 
  2
  check the keys
  --------
  movies.has_key?(:batman)
  =>
  true
  movies.has_key?(:ironman)
  =>
  false
  
  merging
  ---
  movies.merge(malls) { |k,v1,v2| v1 }
  if merge finds any same key in both movies and malls, it will change the key value with v1.
  v1 = movies, v2 = malls
  
  reject
  ----
  movies.reject { |k,v| v.is_a? Integer }
  if reject met the condition, it will rejects the whole key and value pair.
  
 replace
 ----
 movies.replace( {"show" => "no screens" } )
 =>
 replaced the movies hash with the above content
 
 shift
 ---
 remove at the fornt
 movies.shift
 =>
 {}
 slice
 ---
 returns the has with only specified key and value pair
 malls.slice("forum")
 =>
 
 to_a
 ---
 malls.to_a
 which converts the hash into nested array.
 
 raising exception
 -----
 h = Hash.new { |k,v| raise ArgumentError.new("No hash key: #{k}") }
 h[:a] = 4
 h[:b] = 2
 h[:c] = 1
 h[:d] = 3 
 h [:a]
 =>
 4
 h[:e]
 => 
 No hash key: c
 
 sort
 ----
 h.values.sort
 =>
 [1,2,3,4]
 only output have changed not it returns a new hash
 -----
 h.sort_by { |k,v| v }
 => 
 { :c => 1, :b => 2, :d => 2 } 
 
------------------
symbol
--
Only one time created in programming 
name = :velu
name.class
=>
symbol
name.object_id
=>
1111111 #sample
=>
name = "velu"
=>
1122211
name = :velu
name.object_id
=>
1111111
name.capitalize
=>
name.object_id
1111111
---------------