Convert a Ruby Array into the Keys of a New Hash

December 2015

The need to migrate an array into a hash crops up on occasion. The simplest approach is to turn each array item into a hash key pointing at an empty value. A situation where the Ruby Array object's .collect method works great. For example:

-- ruby{numberLines: true}

hash = Hash[array.collect { |item| [item, ""] } ]

Fleshing it out a bit more, here's a full demo showing it in action:

-- ruby{numberLines: true}

#!/usr/bin/env ruby

require 'pp'

array = %w(cat hat bat mat)
hash = Hash[array.collect { |item| [item, ""] } ]

pp array
pp hash

which produces the output showing the original array and then the hash with the desired structure:

-- ruby{numberLines: true}

["cat", "hat", "bat", "mat"]
{"cat"=>"", "hat"=>"", "bat"=>"", "mat"=>""}

Of course, the processing block can assign values as well. For example, changing the above example to use:

-- ruby{numberLines: true}

hash = Hash[array.collect { |item| [item, item.upcase] } ]

would produce the hash with:

-- ruby{numberLines: true}

{"cat"=>"CAT", "hat"=>"HAT", "bat"=>"BAT", "mat"=>"MAT"}

Good stuff.

P.S. Let me know if you have a simpler way to turn ["cat", "hat", "bat", "mat"] into `{"cat"=>"", "hat"=>"", "bat"=>"", "mat"=>""}`.

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