11 - building up a hash using injection.rb

O Reilly Ruby Cookbook source code

collection = [ [1, 'one'], [2, 'two'], [3, 'three'], 
               [4, 'four'], [5, 'five']
             ]
collection.inject({}) do |hash, value|
  hash[value.first] = value.last
  hash
end
# => {5=>"five", 1=>"one", 2=>"two", 3=>"three", 4=>"four"}
#---
collection.dup.inject({}) { |hash, value| hash[value.first] = value.last }
# IndexError: index 3 out of string
#---
Hash.new["key"] = "some value"                            # => "some value"
#---
collection.inject({}) do |hash, value|
  hash.update value.first => value.last
end
# => {5=>"five", 1=>"ontwo", 2=>"two", 3=>"three", 4=>"four"}
#---
class Array
  def to_h(default=nil)
    Hash[ *inject([]) { |a, value| a.push value, default || yield(value) } ]
  end
end
#---
a = [1, 2, 3]

a.to_h(true)
# => {1=>true, 2=>true, 3=>true}

a.to_h { |value| [value * -1, value * 2] }
# => {1=>[-1, 2], 2=>[-2, 4], 3=>[-3, 6]}
#---