performance - How to efficiently sort on 2 string attributes, either of which may be nil, in Ruby? -

class foo   attr_reader :size, :color    def <=>     ...   foo1 = foo.new( size: 'large', color: 'blue'  ) foo2 = foo.new( size: 'small'                 ) foo3 = foo.new( color: 'green'                ) foo4 = foo.new( size: 'small', color: 'red'   )   ... 

size ordered small, nil, medium, large, super-sized. color ordered green, nil, blue, red.

how efficiently sort first size, color?

class foo   attr_reader :size, :color   valid_colors = ["small",nil,"medium","large","super-sized"]   valid_sizes  = ["green", nil, "blue", "red" ]    def size_pos     valid_colors.index(size) || -1   end    def color_pos     valid_sizes.index(color) || -1   end    def initialize(opts={})     @size=opts[:size]     @color=opts[:color]   end    def <=>(other)     [size_pos,color_pos] <=> [other.size_pos, other.color_pos]   end end  foo1 = foo.new( size: 'large', color: 'blue'  ) foo2 = foo.new( size: 'small'                 ) foo3 = foo.new( color: 'green'                ) foo4 = foo.new( size: 'small', color: 'red'   )  [foo1,foo2,foo3,foo4].sort  #[#<foo:0x000000020848d0 @size="small", @color=nil>,   #<foo:0x00000002065700 @size="small", @color="red">,   #<foo:0x00000002074868 @size=nil, @color="green">,   #<foo:0x0000000208da98 @size="large", @color="blue"> ] 

you improve performance extracting out positions class variable hash or constant instead of calling index each time.