Array to Hash Ruby

Question

a = ["item 1", "item 2", "item 3", "item 4"]
h = Hash[*a] # => { "item 1" => "item 2", "item 3" => "item 4" }

That's it. The * is called the splat operator.

One caveat per @Mike Lewis (in the comments): "Be very careful with this. Ruby expands splats on the stack. If you do this with a large dataset, expect to blow out your stack."

So, for most general use cases this method is great, but use a different method if you want to do the conversion on lots of data. For example, @Łukasz Niemier (also in the comments) offers this method for large data sets:

h = Hash[a.each_slice(2).to_a]

Ruby 2.1.0 introduced a to_h method on Array that does what you require if your original array consists of arrays of key-value pairs: http://www.ruby-doc.org/core-2.1.0/Array.html#method-i-to_h.

[[:foo, :bar], [1, 2]].to_h
# => {:foo => :bar, 1 => 2}

Just use Hash.[] with the values in the array. For example:

arr = [1,2,3,4]
Hash[*arr] #=> gives {1 => 2, 3 => 4}

Or if you have an array of [key, value] arrays, you can do:

[[1, 2], [3, 4]].inject({}) do |r, s|
  r.merge!({s[0] => s[1]})
end # => { 1 => 2, 3 => 4 }

This is what I was looking for when googling this:

[{a: 1}, {b: 2}].reduce({}) { |h, v| h.merge v } => {:a=>1, :b=>2}

Enumerator includes Enumerable. Since 2.1, Enumerable also has a method #to_h. That's why, we can write :-

a = ["item 1", "item 2", "item 3", "item 4"]
a.each_slice(2).to_h
# => {"item 1"=>"item 2", "item 3"=>"item 4"}

Because #each_slice without block gives us Enumerator, and as per the above explanation, we can call the #to_h method on the Enumerator object.

You could try like this, for single array

irb(main):019:0> a = ["item 1", "item 2", "item 3", "item 4"]
  => ["item 1", "item 2", "item 3", "item 4"]
irb(main):020:0> Hash[*a]
  => {"item 1"=>"item 2", "item 3"=>"item 4"}

for array of array

irb(main):022:0> a = [[1, 2], [3, 4]]
  => [[1, 2], [3, 4]]
irb(main):023:0> Hash[*a.flatten]
  => {1=>2, 3=>4}