class Array

# File lib/wrandom.rb, line 2
def wsample(*args, &block)
  count, options = \
    if args.size == 0 || args[0].class == Hash
      [nil, args[0]]
    else
      [args[0], args[1]]
    end
  arr = wshuffle(options, &block)
  count ? arr.first(count) : arr.first
end

# File lib/wrandom.rb, line 13
def wshuffle(options = {}, &block)
  sort_by { |v| w_algorithm(v, options, &block) }.reverse!
end

# File lib/wrandom.rb, line 17
def wshuffle!(options = {}, &block)
  sort_by! { |v| w_algorithm(v, options, &block) }.reverse!
end

# File lib/wrandom.rb, line 23
def w_algorithm(v, options = {}, &block)
  # Pavlos S. Efraimidis, Paul G. Spirakis
  # Weighted random sampling with a reservoir
  # Information Processing Letters
  # Volume 97 Issue 5, 16 March 2006
  # Pages 181-185
  r = options[:random] ? options[:random].rand : rand rescue rand
  population = block.call(v)
  r ** ( 1.0 / population )
end