From: Adam Prescott <adam@...>
Date: 2011-09-10T02:13:03+09:00
Subject: Re: Creating a hash from two arrays

On Fri, Sep 9, 2011 at 5:51 PM, simon harrison
<simonharrison.uk@gmail.com> wrote:
> Hi. Can anyone help with this? I'd like to end with a hash like so:
>
> hash = {{"A" => 'alpha'}, {'B' => 'bravo'}} etc...
>
> I'm not sure whether I can use group_by and how to handle case
> insensitity. Cheers for any help.
>
> irb(main):001:0> s = ('A'..'Z').to_a
> => ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
> "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
>
> irb(main):003:0> t = %w(alpha bravo Charlie Zebra)
> => ["alpha", "bravo", "Charlie", "Zebra"]
>

First, {{"A" => "alpha"}, {"B" => "bravo"}} isn't valid syntax. You
probably meant:

{"A" => "alpha", "B" => "bravo", ...}

?

You can indeed use group_by:

>> (("A".."C").to_a + ("a".."c").to_a).group_by { |e| e[0, 1].downcase }
=> {"a"=>["A", "a"], "b"=>["B", "b"], "c"=>["C", "c"]}

Alternatively, if you want to simply map from a[i] to b[i] in a hash,
you can use #zip, #flatten and a splat, in combination with Hash.[]:

>> a = %w[a b c d e]; b = (1..5)

>> c = a.zip(b)
=> [["a", 1], ["b", 2], ["c", 3], ["d", 4], ["e", 5]]

>> c.flatten!
=> ["a", 1, "b", 2, "c", 3, "d", 4, "e", 5]

>> Hash[*c] # equivalent to Hash["a", 1, "b", 2, ...]
=> {"a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5}

Or, in one go:

>> Hash[*a.zip(b).flatten]
=> {"a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5}

Zip, flatten, splat.

This obviously won't let you store multiple elements ("a" => ["a",
"A"]) as in the above approach.