class Array

# File lib/util.rb, line 41
def first_duplicate
  sa = sort
  (1 .. sa.length).argfind { |i| (sa[i] == sa[i - 1]) && sa[i] }
end

# File lib/util.rb, line 50
def flatten_one_level
  inject([]) do |ret, e|
    case e
    when Array
      ret + e
    else
      ret << e
    end
  end
end

# File lib/lowline.rb, line 23
def listify prefix=""
  return "" if empty?
  "\n" +
    map_with_index { |x, i| x.to_s.gsub(/^/, "#{prefix}#{i + 1}. ") }.
      join("\n")
end

# File lib/util.rb, line 46
def to_h
  Hash[*flatten]
end

# File lib/util.rb, line 12
def uniq_by; inject({}) { |h, o| h[yield(o)] = o; h }.values end