Ruby: Sort array of objects after an array of name properties

Question

I have an array "sizes" that look like this:

[#<OPTIONVALUE ID: 5, NAME: "M">,
#<OPTIONVALUE ID: 6, NAME: "M/L">, 
#<OPTIONVALUE ID: 7, NAME: "XS/S">]

Consider the values of attribute NAME. The array is sorted: M, M/L, XS/S.

But the sort order should look like this:

@sizes_sort_order = ["XS", "XS/S", "S", "S/M", "M", "M/L", "L", "L/XL", "XL"]

applied to the former array the order of the elements should look like this:

[#<SPREE::OPTIONVALUE ID: 7, NAME: "XS/S">,
#<SPREE::OPTIONVALUE ID: 5, NAME: "M">,
#<SPREE::OPTIONVALUE ID: 6, NAME: "M/L">]

def sizes
  @sizes ||= grouped_option_values_by_option_type[Spree::OptionType.find_by!(name: 'size')]
  @sizes_sort_order = ["XS", "XS/S", "S", "S/M", "M", "M/L", "L", "L/XL", "XL"]
  @sizes.map { # sort after @size_sort_order }
end

How can i achieve to get the elements in the array sorted after @sizes_sort_order ?

Look at Enumerable#sort_by

Wand Maker
– Wand Maker

2016-07-27 12:10:44 +00:00
Commented Jul 27, 2016 at 12:10 — Wand Maker
– Wand Maker, Commented Jul 27, 2016 at 12:10

Santhosh · Accepted Answer · 2016-07-27 12:33:26Z

3

You can use Enumerable#sort_by

my_array.sort_by {|x| @sizes_sort_order.index(x.name) }

answered Jul 27, 2016 at 12:33

Santhosh

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Comments

nikkypx · Accepted Answer · 2016-07-27 12:42:52Z

You can include the Comparablemodule to get a natural sort for the objects.

http://ruby-doc.org/core-2.2.3/Comparable.html

The Comparable mixin is used by classes whose objects may be ordered. The class must define the <=> operator, which compares the receiver against another object, returning -1, 0, or +1 depending on whether the receiver is less than, equal to, or greater than the other object.

class Size
  include Comparable

  SIZES = ["XS", "XS/S", "S", "S/M", "M", "M/L", "L", "L/XL", "XL"]

  attr_reader :name
  def initialize(id, name)
    @id = id
    @name = name
  end

  def <=>(b)
    SIZES.index(name) <=> SIZES.index(b.name)
  end
end

a = Size.new(5, 'M')
b = Size.new(6, 'M/L')
c = Size.new(7, 'XS/S')

print [a, b, c].sort

[#<Size:0x007f8e910458e0 @id=7, @name="XS/S">, #<Size:0x007f8e910459a8 @id=5, @name="M">, #<Size:0x007f8e91045930 @id=6, @name="M/L">]

Cary Swoveland · Accepted Answer · 2016-07-27 18:12:02Z

This approach involves more steps than ones that employ sort or sort_by, but for larger arrays it may be faster, as no sorting--which is relatively expensive--is involved.

Code

def reorder_by_size(instances, size_order)
  instances.each_with_object({}) { |inst, h| h.update(inst.name=>inst) }.
    values_at(*(size_order & (instances.map { |s| s.name })))
end

Example

First let's create an array of instances of

class Sizes
  attr_reader :name

  def initialize(id, name)
    @id = id
    @name = name
  end
end

like so:

instances = [Sizes.new(5,'M'), Sizes.new(6,'M/L'), Sizes.new(7, 'XS/S')]
  #=> [#<Sizes:0x007fa66a955ac0 @id=5, @name="M">,
  #    #<Sizes:0x007fa66a955a70 @id=6, @name="M/L">,
  #    #<Sizes:0x007fa66a955a20 @id=7, @name="XS/S">]

Then

reorder_by_size(instances, @sizes_sort_order)
 #=> [#<Sizes:0x007fa66a01dfc0 @id=7, @name="XS/S">,
 #    #<Sizes:0x007fa66a86fdb8 @id=5, @name="M">,
 #    #<Sizes:0x007fa66a8404f0 @id=6, @name="M/L">]

Explanation

For instances as defined for the example, first create an array of sizes in the desired order:

names = @sizes_sort_order & (instances.map { |s| s.name })
  #=> ["XS/S", "M", "M/L"]

Important: the doc for Array#& states, "The order is preserved from the original array.".

Now we can create the desired reordering without sorting, by creating a hash with keys the sizes and values the instances, then use Hash#values_at to extract the instances in the desired order.

instances.each_with_object({}) { |inst, h|
  h.update(inst.name=>inst) }.values_at(*names)
  #=> [#<Sizes:0x007fa66a01dfc0 @id=7, @name="XS/S">,
  #    #<Sizes:0x007fa66a86fdb8 @id=5, @name="M">,
  #    #<Sizes:0x007fa66a8404f0 @id=6, @name="M/L">]

The last operation involves the following two steps.

h = instances.each_with_object({}) { |inst, h| h.update(inst.name=>inst) }
  #=> {"M" => #<Sizes:0x007fa66a955ac0 @id=5, @name="M">,
  #    "M/L" => #<Sizes:0x007fa66a955a70 @id=6, @name="M/L">,
  #    "XS/S" => #<Sizes:0x007fa66a955a20 @id=7, @name="XS/S">} 
h.values_at(*names)
  #=> h.values_at(*["XS/S", "M", "M/L"])
  #=> h.values_at("XS/S", "M", "M/L")
  #=> [#<Sizes:0x007fa66a955a20 @id=7, @name="XS/S">,
  #    #<Sizes:0x007fa66a955ac0 @id=5, @name="M">,
  #    #<Sizes:0x007fa66a955a70 @id=6, @name="M/L">]

wow, thanks a lot Cary! For this case i stick to the sort_by solution but for larger arrays I'll choose yours. Awesome explanation by the way.

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