From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-11-20T03:32:23+09:00
Subject: Re: Ternary Operator and Arrays

On Thu, Nov 19, 2009 at 7:16 PM, Felix Dominguez <fdacat@me.com> wrote:
> Given:
> ary = Array.new
> some_hash = {'a' => 1, 'b' => 2, 'c' => 3}
> another_array = ['a', 'c']
>
> Then:
> another_array.each do |x|
>   ary <<  some_hash.has_key?(key) ? ' ' : some_hash[key]
> end
>
> Expected:
> ary should be [1, ' ', 3]
>
> Actual:
> [true, false, true]
>
> Question:
> Why does that happen?

First of all, I assume you copy/pasted wrong, since I get

NameError: undefined local variable or method `key' for main:Object

Assuming you want to query the hash for each value of the
another_array, you can do this:

irb(main):025:0> another_array.each do |x|
irb(main):026:1* ary <<  (some_hash.has_key?(x) ? ' ' : some_hash[x])
irb(main):027:1> end
=> ["a", "c"]
irb(main):028:0> ary
=> [" ", " "]

Please note the parenthesis.
And I have the suspicion that you have the logic backwards, since you
return " " when the hash has the key, and go to the hash when it
doesn't (which will always return nil or the default value). Maybe you
wanted this:

irb(main):033:0> ary = []
=> []
irb(main):034:0> another_array.each do |x|
irb(main):035:1* ary << (some_hash.has_key?(x) ? some_hash[x]: ' ')
irb(main):036:1> end
=> ["a", "c"]
irb(main):037:0> ary
=> [1, 3]

Another way of doing this, more idiomatic would be:

irb(main):038:0> ary = another_array.map {|x| some_hash.has_key?(x) ?
some_hash[x]: ' '}
=> [1, 3]
irb(main):039:0> ary
=> [1, 3]


But anyway, you won't get a three element array, since you are
iterating over another_array, which has only two entries. Can you
explain how you should obtain 3 elements in the array? Is it all
elements in the hash that have their key in the another_array? If so:

irb(main):040:0> ary = some_hash.map {|k,v| another_array.include?(k) ? v : ' '}
=> [1, " ", 3]

Hope this helps,

Jesus.