Sorting an array of objects in Ruby by object attribute?

Question

I have an array of objects in Ruby on Rails. I want to sort the array by an attribute of the object. Is it possible?

Answer 1

in case you need sorting by two attributes, where first one is more important then second (means taking in account second arguments only if first arguments are equal), then you may do like this

myarray.sort{ |a,b| (a.attr1 == b.attr1) ? a.attr2 <=> b.attr2 : a.attr1 <=> b.attr1 }

or in case of array of arrays

myarray.sort{ |a,b| (a[0] == b[0]) ? a[1] <=> b[1] : a[0] <=> b[0] }

Answer 2

I recommend using sort_by instead:

objects.sort_by {|obj| obj.attribute}

Especially if attribute may be calculated.

Or a more concise approach:

objects.sort_by(&:attribute)

Answer 3

More elegant objects.sort_by(&:attribute), you can add on a .reverse if you need to switch the order.

Answer 4

Array#sort works well, as posted above:

myarray.sort! { |a, b|  a.attribute <=> b.attribute }

BUT, you need to make sure that the <=> operator is implemented for that attribute. If it's a Ruby native data type, this isn't a problem. Otherwise, write you own implementation that returns -1 if a < b, 0 if they are equal, and 1 if a > b.

Answer 5

Yes its possible

http://ariejan.net/2007/01/28/ruby-sort-an-array-of-objects-by-an-attribute/

Answer 6

You can make any class sortable by overriding the <=> method:

class Person

  attr_accessor :first_name, :last_name

  def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
  end

  def <=>(other)
    @last_name + @first_name <=> other.last_name + other.first_name
  end

end

Now an array of Person objects will be sortable on last_name.

ar = [Person.new("Eric", "Cunningham"), Person.new("Homer", "Allen")]

puts ar  # => [ "Eric Cunningham", "Homer Allen"]  (Person objects!)

ar.sort!

puts ar  # => [ "Homer Allen", "Eric Cunningham" ]