What is the best way to convert an array to a hash in Ruby
Simply use Hash[*array_variable.flatten]
For example:
a1 = ['apple', 1, 'banana', 2]h1 = Hash[*a1.flatten(1)]puts "h1: #{h1.inspect}"a2 = [['apple', 1], ['banana', 2]]h2 = Hash[*a2.flatten(1)]puts "h2: #{h2.inspect}"
Using Array#flatten(1)
limits the recursion so Array
keys and values work as expected.
NOTE: For a concise and efficient solution, please see Marc-André Lafortune's answer below.
This answer was originally offered as an alternative to approaches using flatten, which were the most highly upvoted at the time of writing. I should have clarified that I didn't intend to present this example as a best practice or an efficient approach. Original answer follows.
Warning! Solutions using flatten will not preserve Array keys or values!
Building on @John Topley's popular answer, let's try:
a3 = [ ['apple', 1], ['banana', 2], [['orange','seedless'], 3] ]h3 = Hash[*a3.flatten]
This throws an error:
ArgumentError: odd number of arguments for Hash from (irb):10:in `[]' from (irb):10
The constructor was expecting an Array of even length (e.g. ['k1','v1,'k2','v2']). What's worse is that a different Array which flattened to an even length would just silently give us a Hash with incorrect values.
If you want to use Array keys or values, you can use map:
h3 = Hash[a3.map {|key, value| [key, value]}]puts "h3: #{h3.inspect}"
This preserves the Array key:
h3: {["orange", "seedless"]=>3, "apple"=>1, "banana"=>2}
The best way is to use Array#to_h
:
[ [:apple,1],[:banana,2] ].to_h #=> {apple: 1, banana: 2}
Note that to_h
also accepts a block:
[:apple, :banana].to_h { |fruit| [fruit, "I like #{fruit}s"] } # => {apple: "I like apples", banana: "I like bananas"}
Note: to_h
accepts a block in Ruby 2.6.0+; for early rubies you can use my backports
gem and require 'backports/2.6.0/enumerable/to_h'
to_h
without a block was introduced in Ruby 2.1.0.
Before Ruby 2.1, one could use the less legible Hash[]
:
array = [ [:apple,1],[:banana,2] ]Hash[ array ] #= > {:apple => 1, :banana => 2}
Finally, be wary of any solutions using flatten
, this could create problems with values that are arrays themselves.