class Array

Loops through the items in the array and counts the number of times each item appears. If a block is provided, each item is passed into the block, and the result of yielding the block is counted instead.

@return [Hash] A hash whose keys are the items in the

array or the results of yielding the block, and whose values are the
number of times each item appeared in the array.

@example Find the number of times each item appears in the array.

items  = %w(foo foo foo bar bar baz wibble wobble)
items.fold
#=> { 'foo' => 3, 'bar' => 2, 'baz' => 1, 'wibble' => 1, 'wobble' => 1 }

@example Count the items in the array with each status value.

class SampleItem < Struct.new(:status); end
items = [
  SampleItem.new :approved,
  SampleItem.new :rejected,
  SampleItem.new :approved,
  SampleItem.new :approved,
  SampleItem.new :error,
  SampleItem.new nil,
  SampleItem.new :rejected,
] # end array
items.fold { |item| item.status }
#=> { :approved => 3, :rejected => 2, :error => 1, nil => 1 }

@since 0.1.0

# File lib/sleeping_king_studios/ext/array/fold.rb, line 34
def fold
  each.with_object({}) do |item, hsh|
    value = block_given? ? yield(item) : item
    hsh[value] = hsh.fetch(value, 0) + 1
  end # each with object
end