Ruby, how to create a hash from two arrays?

Question

I'm fairly a beginner in Ruby and I'm trying to do the following: Let's say I have two arrays:

array_1 = ["NY", "SF", "NL", "SY"]
array_2 = ["apple", "banana"]

I want to merge the arrays to a hash so each object in array_1 will be assigned with the objects in array_2

Thanks in advance.

The arrays are different lengths so it isn't clear what the resultant Hash should look like. — mu is too short
– mu is too short, Commented Nov 24, 2015 at 17:18
Best not to post a question and walk away, as it my not be as clear as you think it is, especially considering that you are new to Ruby. Please edit to add the desired result (as opposed to doing that in a comment). — Cary Swoveland
– Cary Swoveland, Commented Nov 24, 2015 at 20:31

ndnenkov · Accepted Answer · 2015-11-24 17:46:55Z

6

x = [:foo, :bar, :baz]
y = [1, 2, 3]
x.zip(y).to_h # => {:foo=>1, :bar=>2, :baz=>3}

answered Nov 24, 2015 at 17:46

ndnenkov

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2 Comments

Cary Swoveland Over a year ago

This implies that { "NY"=>"apple", "SF"=>" banana", "NL"=nil, "SY"= nil } is the desired result. I may be wrong, but I think you have answered a different question.

ndnenkov Over a year ago

@CarySwoveland, who knows :)

humza · Accepted Answer · 2015-11-24 17:32:16Z

2

You can use the zip method, like so:

Hash[array_2.zip(array_1)]

answered Nov 24, 2015 at 17:32

humza

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1 Comment

Cary Swoveland Over a year ago

This returns { 'apple'=>'NY', 'banana'=>'SF' }. How does that satisfy the requirement that "each object in array_1 will be assigned with the objects in array_2"?

Cary Swoveland · Accepted Answer · 2015-11-24 18:04:53Z

h = array_1.product([array_2]).to_h
  #=> {"NY"=>["apple", "banana"], "SF"=>["apple", "banana"],
  #    "NL"=>["apple", "banana"], "SY"=>["apple", "banana"]}

We were given Array#to_h in MRI v2.0. For earlier versions, use Kernel#Hash:

h = Hash[array_1.product([array_2])]

but beware:

array_2[0] = "cat"
array_2
  #=> ["cat", "banana"] 
h #=> {"NY"=>["cat", "banana"], "SF"=>["cat", "banana"],
  #    "NL"=>["cat", "banana"], "SY"=>["cat", "banana"]}

You may instead want:

h = array_1.each_with_object({}) { |str,h| h[str] = array_2.dup }
  #=> {"NY"=>["apple", "banana"], "SF"=>["apple", "banana"],
  #    "NL"=>["apple", "banana"], "SY"=>["apple", "banana"]}

array_2[0] = "cat"
h #=> {"NY"=>["apple", "banana"], "SF"=>["apple", "banana"],
  #    "NL"=>["apple", "banana"], "SY"=>["apple", "banana"]}

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