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comp.lang.ruby

Hash.from_zipped_array

Farrel Lifson

3/1/2006 2:19:00 AM

Hi folks,

Array has got a pretty cool method zip which 'zips' two arrays together like so:

[1,2,3].zip([2,4,6])
=> [[1,2],[2,4],[3,6]]

That's also what you get when you call to_a on a Hash like
{1=>2,2=>4,3=>6}, so I thought why not add a method to Hash to do the
reverse, that is to construct a Hash from a zipped array?

class Hash
def Hash.from_zipped_array(zipped_array)
zipped_array.inject({}) do |hash,key_value_pair|
hash[key_value_pair[0]] =key_value_pair[1]
hash
end
end
end

# Example usage
animal = ["dog","cat",bird"]
sound = ["woof,"meow","cheep"]

make_a_sound_like_a = Hash.from_zipped_array(animal.zip(sound)
make_a_sound_like_a["dog"]
=>"woof"

Useful enough for inclusion?

Farrel
10 Answers

Ara.T.Howard

3/1/2006 2:40:00 AM

0

Farrel Lifson

3/1/2006 7:41:00 PM

0

Is there anything they haven't thought of in the API? They still keep
suprising me...

dblack

3/1/2006 8:31:00 PM

0

James Gray

3/1/2006 8:54:00 PM

0

On Mar 1, 2006, at 2:31 PM, dblack@wobblini.net wrote:

> Hi --
>
> On Wed, 1 Mar 2006, ara.t.howard@noaa.gov wrote:
>
>> it's pretty dang easy to do already:
>>
>> harp:~ > cat a.rb
>> animal, sound = %w[dog cat bird], %w[woof meow cheep]
>> require 'yaml' and y Hash[*animal.zip(sound).flatten]
>>
>>
>> harp:~ > ruby a.rb
>> ---
>> cat: meow
>> bird: cheep
>> dog: woof
>
> A good opportunity for my annual plug for the flattenx extension :-)
> (On RAA, still, I think.) It lets you flatten by any number of
> levels, so that you can use that technique even with nested arrays.

It's not too hard to allow nested Arrays in Hash construction even
without the library:

>> arr = [[:one, 1], [:two, %w{an Array}], [:three, 2]]
=> [[:one, 1], [:two, ["an", "Array"]], [:three, 2]]
>> Hash[*arr.inject(Array.new) { |args, a| args.push(*a) }]
=> {:two=>["an", "Array"], :three=>2, :one=>1}

James Edward Gray II

dblack

3/1/2006 9:12:00 PM

0

Christian Neukirchen

3/1/2006 9:36:00 PM

0

dblack@wobblini.net writes:

> Hi --
>
> On Wed, 1 Mar 2006, ara.t.howard@noaa.gov wrote:
>
>> it's pretty dang easy to do already:
>>
>> harp:~ > cat a.rb
>> animal, sound = %w[dog cat bird], %w[woof meow cheep]
>> require 'yaml' and y Hash[*animal.zip(sound).flatten]
>>
>>
>> harp:~ > ruby a.rb
>> ---
>> cat: meow
>> bird: cheep
>> dog: woof
>
> A good opportunity for my annual plug for the flattenx extension :-)
> (On RAA, still, I think.) It lets you flatten by any number of
> levels, so that you can use that technique even with nested arrays.

Try to get that into 2.0, at least flatten_once. *please*.

> David
--
Christian Neukirchen <chneukirchen@gmail.com> http://chneuk...

Ara.T.Howard

3/1/2006 10:33:00 PM

0

Yukihiro Matsumoto

3/1/2006 11:25:00 PM

0

Hi,

In message "Re: Hash.from_zipped_array"
on Thu, 2 Mar 2006 06:12:08 +0900, dblack@wobblini.net writes:

|I may be in the minority, but I prefer:
|
| Hash[*arr.flatten_once]
|
|:-)

I'm not sure above is the best solution, but anyway giving #flatten a
level argument could be useful, so that you can do:

Hash[*arr.flatten(1)]

It's more general, and even shorter.

matz.

dblack

3/1/2006 11:44:00 PM

0

Joel VanderWerf

3/2/2006 12:06:00 AM

0

ara.t.howard@noaa.gov wrote:
> On Thu, 2 Mar 2006, Christian Neukirchen wrote:
...
>> Try to get that into 2.0, at least flatten_once. *please*.
>
> agreed. however i'd strongly go with an api like
>
>
> -a

Is that the sound of one API clapping? ;)

Seriously, I cast my vote for flatten having an optional level argument.
(Couldn't this go in 1.8.5. since it wouldn't break anything?)

--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407