Question

What is a good way of sorting section number strings in Ruby. For example:

sections = ["10", "3", "4", "5", "6", "7", "8", "9", "2", "1", "1.1", "1.1.1", "1.1.2"]
# ["1", "1.1", "1.1.1", "1.1.2", "2", "3", "4", "5", "6", "7", "8", "9", "10"]

Answer 1

If you have to deal with arbitrarily nested subsections then you could do something like this:

sections = ["10", "3", "4", "5", "6", "7", "8", "9", "2", "1", "1.1", "1.2", "1.2.5"]
sections.sort! { |a,b| a.split('.').map(&:to_i) <=> b.split('.').map(&:to_i) }

That implementation isn’t exactly quick due to the repeated split and map but you could roll your own Schwartzian Transform if it was too slow:

sections.map  { |e| [e, e.split('.').map(&:to_i) ] } \
        .sort { |a, b| a.last <=> b.last } \
        .map  { |e| e.first }

Note that Enumerable#sort_by does an internal Schwartzian Transform for you:

The current implementation of sort_by generates an array of tuples containing the original collection element and the mapped value.

So you could also let sort_by take care of some of the ugliness:

section.sort_by { |e| e.split('.').map(&:to_i) }

and get something that is pretty easy to understand at a glance.