From: Nathan Clark <tokenshift@...>
Date: 2010-11-13T01:07:47+09:00
Subject: Re: help sorting objects by their instance field

Check the docs for class Array
http://ruby-doc.org/core/classes/Array.html#M002185

You can pass a block to array.sort, that tells it what to sort by (in
your case, person.lname).

On Fri, Nov 12, 2010 at 10:43 AM, Aaron Haas <aaron4osu@gmail.com> wrote:
> 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]
>
> --
> Posted via http://www.ruby-forum.com/.
>
>