Sorting an array of objects in Ruby by object attribute?

Question

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)

Yes, using Array#sort! this is easy.

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

Ascending order :

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

or

objects_array.sort_by{ |obj| obj.attribute }

Descending order :

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

or

objects_array.sort_by{ |obj| obj.attribute }.reverse

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] }

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" ]