From: google@... (Tom Payne)
Date: 2002-10-18T00:27:23+09:00
Subject: Enumerable.partition

Hi --

I see that Enumerable.partition has been added somewhere between 1.6.7
and 1.7.3. It's implemention is equivilent to

module Enumerable
  def partition
    result = [[], [[]]
    each do |value|
      result[yield(value) ? 0 : 1].push(value)
    end
    result
  end
end

e.g. [0, 1, 2, 3].new_parition { |x| x > 1 }
gives [[2, 3], [0, 1]]

Please (pretty please) can this be changed to the much more powerful:

module Enumerable
  def new_partition(default = nil)
    result = Hash.new(default)
    each do |value|
      key = yield(value)
      if result.has_key?(key)
        result[key].push(value)
      else
        result[key] = [value]
      end
    end
    result
  end
end

e.g. [0, 1, 2, 3].new_partition { |x| x > 1 }
gives {false=>[0, 1], true=>[2, 3]}

Hopefully this won't break too much code in 1.7.3. It's very useful:

[-2, -1, 0, 1, 2].new_partition { |x| x <=> 0 }
# => {0=>[0], 1=>[1, 2], -1=>[-2, -1]}

The ability to override the hash default is helpful:

a = [0, 1, 2]
h = a.partition([]) { |x| x <=> 0 }
# => {0=>[0], 1=>[1, 2]}
puts("there are #{h[-1].size} negative numbers in a")

Thanks,

Tom