From: Yossef Mendelssohn <ymendel@...>
Date: 2008-05-14T00:14:01+09:00
Subject: Re: hash merge

On May 13, 9:48 am, Tim Wolak <tim.wo...@gmail.com> wrote:
> I'm not sure if I'm using this the right way and I'm hoping you guys can
> help.
>
> I am merging two hashes together using merge and need to keep the keys
> the same and subtract the difference between the two values.  The keys
> are account numbers and the values are the balances.  Not sure why the
> balances are not subtracting and creating the new value.
>
> Thanks in advance.
> Tim
>
>  class Calculate
>   attr_reader :sktyfuta, :sktyfutb
>   def initialize(sktyfuta, sktyfutb)
>     @sktyfuta = sktyfuta
>     @sktyfutb = sktyfutb
>   end
>
>   def data_comp
>       @sktyfuta.merge(@sktyfutb) { |key, old_value, new_value| old_value
> - new_value }
>   end
> end
> --
> Posted viahttp://www.ruby-forum.com/.

I'm not finding that to be the case.

>> a = {:a => 1, :b => 2}
=> {:a=>1, :b=>2}
>> b = {:b => 0, :c => 3}
=> {:c=>3, :b=>0}
>> a.merge b
=> {:c=>3, :a=>1, :b=>0}
>> a.merge(b) { |key, old, new|  old - new }
=> {:c=>3, :a=>1, :b=>2}

and with your code:

>>  class Calculate
>>   attr_reader :sktyfuta, :sktyfutb
>>   def initialize(sktyfuta, sktyfutb)
>>     @sktyfuta = sktyfuta
>>     @sktyfutb = sktyfutb
>>   end
>>
>>   def data_comp
>>       @sktyfuta.merge(@sktyfutb) { |key, old_value, new_value| old_value - new_value }
>>   end
>> end
=> nil
>> c = Calculate.new(a, b)
=> #<Calculate:0x579cc @sktyfutb={:c=>3, :b=>0},
@sktyfuta={:b=>2, :a=>1}>
>> c.data_comp
=> {:c=>3, :a=>1, :b=>2}

Thanks for teaching me about Hash#merge with a block, by the way.

--
-yossef