Attempt to discern number of spaces used for an indent across a set of source files.

dentdetect.rb

class Array
  def freq_by &block
    group_by(&block).map {|k,v| [k, v.count] }.sort_by(&:first)
  end

  def freq
    freq_by {|e| e }
  end
end

puts ARGF.lines.map {|l| l.split(/\S/).first }
               .compact
               .select {|s| s.length > 1 }
               .select {|s| s.chars.all? {|c| c == ' ' }}
               .freq
               .sort_by {|_,c| -c }
               .take(10)
               .map {|p,_| p.length }
               .sort
               .each_cons(2)
               .take_while {|l,r| l.gcd(r) > 1 }
               .map(&:first)
               .reduce(&:gcd)