favorite_ruby_methods_1.rb

# Arrays

# Array#reverse_each
# Just like Array#each, but reversed. 
# This saves having to reverse an array if trying to iterate from the end

  a = [1, 2, 3, 4]
  str = ""
  a.reverse_each{ |n| str += n.to_s } # str => "4321"
    
# Array.new
# This has some powerful extra features and some potential dangers
# For example, we can pass to a block to create an array populated with elements 
# calculated from their respective indicies

  Array.new(4){ |index| index * 2 + 1 } # => [1, 3, 5, 7]
    
  # But be careful!
  arr = Array.new(2, Hash.new)  # => [{}, {}]
   
  arr[0]['name'] = 'bob'
  arr # => [{"name" => "bob"}, {"name" => "bob"}]
  
  # The above example creates an array with each element referencing THE SAME hash.
  # If you want multiple hashes, you must pass a block
  
  arr = Array.new(2) { Hash.new }
  arr[0]['name'] = 'bob'
  arr # => [{"name"=>"bob"}, {}]
  
# Array#clear
# Clears all elements from array

  arr = [1, 2, 3]
  arr.clear
  arr # => []
  
# Array#map in conjunction with Enumerable#with_index

  arr = [1, 2, 3]
  arr_new = arr.map.with_index { |element, index| element * index }
  arr_new # => [0, 2, 6]
  
  # passing an offset argument to with_index
  arr_new = arr.map.with_index(2) { |element, index| element * index }
  arr_new # => [2, 6, 12]
  
  # I'm still trying to fully understand how Enumerable objects work, but here is the gist:
  # arr.map creates and Enumerable object. The with_index function is a method of the 
  # Enumerable class, so we can call this on arr.map.
  
  # When Enumerable#with_index is called on arr.map, it wraps the enumerable object returned 
  # by arr.map in a second enumerable object, specified by an index.
  # This then allows the index and elements to be accessed by the following block. I'm still 
  # trying to work out the details about how this actually works under the hood
  
# Array#flatten
# Flattens multidimensional arrays

  arr = [1, 2, [3, 4, 5], [1, 3]]
  arr.flatten # => [1, 2, 3, 4, 5, 1, 3]
  
  # Flatten also has a destructive twin: Array#flatten!