How to sort array elements in lexicographic order in Ruby

Question

I have an array

arr = [[1,2],[2,3],[2,1],[0,1]]

I would like them to be in order:

arr = [[0,1],[1,2],[2,1],[2,3]]

I would like to use Ruby's sort_by method to do this. How could I sort an array of arrays on two levels in Ruby like this?

Answer 1

Array#sort sorts sub-arrays lexicographically by default (see Array#<=> ). You don't need to define anything:

[[1,2],[2,3],[2,1],[0,1]].sort
# => [[0, 1], [1, 2], [2, 1], [2, 3]]

If you really want to use sort_by :

[[1,2],[2,3],[2,1],[0,1]].sort_by(&:itself)
# => [[0, 1], [1, 2], [2, 1], [2, 3]]

Answer 2

If you consider each element of the subarray to be a digit from 0 to 9, you could use Array#sort_by , where the block converts the array into string then into integer:

arr.sort_by { |e| e.join.to_i }

#=> [[0, 1], [1, 2], [2, 1], [2, 3]]

---

How it works.

 [1, 2].join #=> "12" [1, 2].join.to_i #=> 12 

---

In this case:

 arr = [[1,0,2,0],[2,3],[2,1],[0,1]] #=> [[0, 1], [2, 1], [2, 3], [1, 0, 2, 0]]