ProjectionOperators

Projection operators¶ ↑

• Simple 1

  numbers = [ 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 ]
  output =  _{ 
    from n
    in_ numbers
    select n + 1
  }.to_a
  output.should == [6, 5, 2, 4, 10, 9, 7, 8, 3, 1

• Simple 2

  Product = Struct.new(:name, :price)
  products = [Product.new("shoes", 1.75), Product.new("glasses", 55.55), Product.new("pencil", 5.20)]
  
  product_names = _{
    from p
    in_ products 
    select p.name
  }.to_a
  product_names.should == ["shoes","glasses",

• Select - Transformation

  numbers = [ 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 ]
  strings = [ "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" ]
  text_nums = _{
    from n
    in_ numbers
    select strings[n]
  }.to_a
  text_nums.should == ["five", "four", "one", "three", "nine", "eight", "six", "seven", "two", "zer