From: Aaron Haas <aaron4osu@...>
Date: 2010-11-13T00:43:17+09:00
Subject: help sorting objects by their instance field

I'm trying to figure out how to sort objects in an array by one of their
instance
variables, in this case last name. The person class has a first name,
last name, and an address object. The address book class is made up of
an array of persons. How do I sort the array of persons in
alphabetically by the persons last name instance fields. I added a
getLastname method to the persons class, but I'm not sure on the logic.

[CODE]
class Person
    attr_accessor :fname, :lname, :address

    # initializer
    def initialize
        @fname = @lname = ""
        # since address is an object
        @address = Address.new
    end

    # assign given values to Person object
    def crPerson (aFname, aLname, aAddress)
        @fname = aFname
        @lname = aLname
        @address = aAddress
    end

    def get_lname
        return @lname
    end

     # string representation of Person
     # note the syntax: address.to_s (to call the to_s instance method
of Address class)
    def to_s
        @fname + " " + @lname + "\n" + "\n" + address.to_s
    end

end
[/CODE]

[CODE]
class AddressBook

    # class variable. keeps track of number of address book entries
    @@instances = 0

    # no attr_accessor
    # don't want the user to have direct access to @persons
    def initialize
        @persons = [] # starts with empty array
    end

    # add person to address book
    def add(person)
        @persons += [person]
        @@instances += 1
    end

    # delete person from address book
    def remove(person)
        @persons.delete(person)
        @@instances -= 1
    end
     #  totally lost on this part
    # print sorted by last name method using person's get_lname method
    def print_addresses
      @persons.each { |p| persons[p].get_lname.sort  }
      end # close while loop
      # print sorted array
      @persons.each { |p| yield p }
    end

end
[/CODE]

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