Forum: Ruby "adding" two hashes

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Bryson S. (Guest)
on 2009-01-28 21:09
Hi,

I'm wondering if it is possible to "add" the values of two hashes
together.  Suppose I had:

hash1 = {:key_one=>100, :key_two=>200}
hash2 = {:key_two=>300, :key_three=>400}

I'd like to "add" the hashes together so that I get

result => {:key_one=>100, :key_two=>500, :key_three=>400}

Do I need to write my own function to parse through each hash's keys?
Is there a built-in way to do this?

Thanks!
Ben B. (Guest)
on 2009-01-28 21:23
(Received via mailing list)
On Wed, Jan 28, 2009 at 11:07 AM, Bryson S. 
<removed_email_address@domain.invalid>
wrote:
> Do I need to write my own function to parse through each hash's keys?
> Is there a built-in way to do this?

You can try Hash#merge:

irb(main):007:0> a = {:a => 1}
=> {:a=>1}
irb(main):008:0> b = {:b => 2}
=> {:b=>2}
irb(main):009:0> c = a.merge( b )
=> {:a=>1, :b=>2}

Note that if you have duplicate keys, the values in b will override
the values in a.

Ben
Rob B. (Guest)
on 2009-01-28 21:31
(Received via mailing list)
On Jan 28, 2009, at 2:07 PM, Bryson S. wrote:

> result => {:key_one=>100, :key_two=>500, :key_three=>400}
>
> Do I need to write my own function to parse through each hash's keys?
> Is there a built-in way to do this?
>
> Thanks!


irb> hash1 = {:key_one=>100, :key_two=>200}
=> {:key_two=>200, :key_one=>100}
irb> hash2 = {:key_two=>300, :key_three=>400}
=> {:key_two=>300, :key_three=>400}

irb> result = hash1.merge(hash2) {|key,val1,val2| val1+val2}
=> {:key_two=>500, :key_three=>400, :key_one=>100}

You only have to write the block that deals with the duplicates for
'key'

-Rob

Rob B.    http://agileconsultingllc.com
removed_email_address@domain.invalid
Tim H. (Guest)
on 2009-01-28 21:33
Bryson S. wrote:
> Hi,
>
> I'm wondering if it is possible to "add" the values of two hashes
> together.  Suppose I had:
>
> hash1 = {:key_one=>100, :key_two=>200}
> hash2 = {:key_two=>300, :key_three=>400}
>
> I'd like to "add" the hashes together so that I get
>
> result => {:key_one=>100, :key_two=>500, :key_three=>400}
>
> Do I need to write my own function to parse through each hash's keys?
> Is there a built-in way to do this?
>
> Thanks!

No built-in way, but it would be easy to use hash1.each_key to iterate
over the keys of hash1. For every key in hash1, get its value for that
key from hash1 and hash2, add the two values and store the sum as the
value of that key in result.

The question is, what happens if there's a key in hash1 that isn't in
hash2, or vice versa?
Rob B. (Guest)
on 2009-01-28 22:13
(Received via mailing list)
On Jan 28, 2009, at 2:31 PM, Tim H. wrote:

>>
> value of that key in result.
>
> The question is, what happens if there's a key in hash1 that isn't in
> hash2, or vice versa?

In case it was missed the first time:

irb> result = hash1.merge(hash2) {|key,val1,val2| val1+val2}
=> {:key_two=>500, :key_three=>400, :key_one=>100}

You only have to write the block that deals with the duplicates for
'key'

-Rob

Rob B.    http://agileconsultingllc.com
removed_email_address@domain.invalid
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