From: SpringFlowers AutumnMoon <summercoolness@...>
Date: 2007-09-23T20:49:27+09:00
Subject: quick way for total count of a Hash object or a Tally class

for the hash

["apple" => 3, "banana" => 2]

is there an instant way to tally up all the counts?  (instead of looping
through all keys and add up all counts, because the hash can be very
big, like thousands of items, and looping can be quite expensive for CPU
time)

does the following look right?

class Tally < Hash

 attr_reader :total

 def initialize
   @total = 0
   super(0)
 end

 def []=(key, new_value)
   @total -= self[key]   # previous value goes
   @total += new_value   # new value in

   super
 end

 def inspect
   super + "  total = #{@total}"
 end

end

t = Tally.new

t["apple"] += 1

puts; p t

t["banana"] += 1

puts; p t

t["banana"] = 1000

puts; p t

t["apple"] += 10

puts; p t

t["apple"] -= 5

puts; p t

t["apple"] = 10000

puts; p t

t[123] = 10

puts; p t


[~/depot] 360 $ ruby test_tally.rb

{"apple"=>1}  total = 1

{"apple"=>1, "banana"=>1}  total = 2

{"apple"=>1, "banana"=>1000}  total = 1001

{"apple"=>11, "banana"=>1000}  total = 1011

{"apple"=>6, "banana"=>1000}  total = 1006

{"apple"=>10000, "banana"=>1000}  total = 11000

{"apple"=>10000, 123=>10, "banana"=>1000}  total = 11010
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