Convert Array to Hash While Preserving Array Index Values in Ruby

Convert Array to Hash while preserving Array index values in Ruby

Using Enumerable#each_with_index:

Hash[array.each_with_index.map { |value, index| [index, value] }]
# => {0=>"Adult", 1=>"Family", 2=>"Single", 3=>"Child"}

As @hirolau commented, each_with_index.map can also be written as map.with_index.

Hash[array.map.with_index { |value, index| [index, value] }]
# => {0=>"Adult", 1=>"Family", 2=>"Single", 3=>"Child"}

UPDATE

Alterantive that use Hash#invert:

Hash[array.map.with_index{|*x|x}].invert
# => {0=>"Adult", 1=>"Family", 2=>"Single", 3=>"Child"}
Hash[[*array.map.with_index]].invert
# => {0=>"Adult", 1=>"Family", 2=>"Single", 3=>"Child"}

Convert an array into an index hash in Ruby

If all you need the hash for is membership, consider using a Set:

Set

Set implements a collection of unordered values with no
duplicates. This is a hybrid of Array's intuitive inter-operation
facilities and Hash's fast lookup.

Set is easy to use with Enumerable objects (implementing
each). Most of the initializer methods and binary operators accept
generic Enumerable objects besides sets and arrays. An
Enumerable object can be converted to Set using the
to_set method.

Set uses Hash as storage, so you must note the following points:

• Equality of elements is determined according to Object#eql? and Object#hash.
• Set assumes that the identity of each element does not change while it is stored. Modifying an element of a set will render the set to an
  unreliable state.
• When a string is to be stored, a frozen copy of the string is stored instead unless the original string is already frozen.

Comparison

The comparison operators <, >, <= and >= are implemented as
shorthand for the {proper_,}{subset?,superset?} methods. However, the
<=> operator is intentionally left out because not every pair of
sets is comparable. ({x,y} vs. {x,z} for example)

Example

require 'set'
s1 = Set.new [1, 2]                   # -> #<Set: {1, 2}>
s2 = [1, 2].to_set                    # -> #<Set: {1, 2}>
s1 == s2                              # -> true
s1.add("foo")                         # -> #<Set: {1, 2, "foo"}>
s1.merge([2, 6])                      # -> #<Set: {1, 2, "foo", 6}>
s1.subset? s2                         # -> false
s2.subset? s1                         # -> true

[...]

Public Class Methods

new(enum = nil)

Creates a new set containing the elements of the given enumerable
object.

If a block is given, the elements of enum are preprocessed by the
given block.

What is the best way to convert an array to a hash in Ruby

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.

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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}

ruby convert array to hash preserve duplicate key

I hope you would like this :

ary = [
       "19d97e408ee3f993745b053e281ac9dc69519e06","refs/heads/auto",
       "8f6f47c6e8023540b022586e368c68e1e814ce6d","refs/heads/callout_hooks",  
       "3cbdb4b2fcb85bc7f0ed08b62e2bf2445a7659e8","refs/heads/elab",
       "d38a9a26ef887c08b306bdab210b39882f58e587","refs/heads/elab_6.1",
       "19d97e408ee3f993745b053e281ac9dc69519e06","refs/heads/master",
       "906dfe6eebff832baf0f92683d751432fcc98ab7","refs/heads/regression"
     ]

array_hash = ary.each_slice(2).with_object(Hash.new { |h,k| h[k] = []}) do |(k,v),hash|
  hash[k] << v 
end

# the main advantage is here you wouldn't loose any data, all are with you. You can
# use it as per your need. I think it is a better approach to deal with your situation.
array_hash
# => {"19d97e408ee3f993745b053e281ac9dc69519e06"=>
#      ["refs/heads/auto", "refs/heads/master"],
#     "8f6f47c6e8023540b022586e368c68e1e814ce6d"=>["refs/heads/callout_hooks"],
#     "3cbdb4b2fcb85bc7f0ed08b62e2bf2445a7659e8"=>["refs/heads/elab"],
#     "d38a9a26ef887c08b306bdab210b39882f58e587"=>["refs/heads/elab_6.1"],
#     "906dfe6eebff832baf0f92683d751432fcc98ab7"=>["refs/heads/regression"]}

Convert an array to hash, where keys are the indices

arr = ["one", "two", "three", "four", "five"]

x = Hash[(0...arr.size).zip arr]
# => {0=>"one", 1=>"two", 2=>"three", 3=>"four", 4=>"five"}

How to convert an array to a hash with specified common values

There are many ways, e.g.:

arr.zip([{}] * arr.size).to_h

or (the latter, thx @Stefan, is not probably what you wanted, since it will share one hash for all keys):

arr.product([{}]).to_h

Convert an Array of Strings to a Hash in Ruby

You could do this:

arr = ["First Name", "Last Name", "Location", "Description"]

letter = Enumerator.new do |y|
  l = ('A'.ord-1).chr
  loop do
    y.yield l=l.next
  end
end
  #=> #<Enumerator: #<Enumerator::Generator:0x007f9a00878fd8>:each> 

h = arr.each_with_object({}) { |s,h| h[letter.next] = s }
  #=> {"A"=>"First Name", "B"=>"Last Name", "C"=>"Location", "D"=>"Description"} 

h.invert
  #=> {"First Name"=>"A", "Last Name"=>"B", "Location"=>"C", "Description"=>"D"} 

or

letter = ('A'.ord-1).chr
  #=> "@" 
h = arr.each_with_object({}) { |s,h| h[letter = letter.next] = s }
  #=> {"A"=>"First Name", "B"=>"Last Name", "C"=>"Location", "D"=>"Description"} 

When using the enumerator letter, we have

27.times { puts letter.next }
  #=> "A"
  #   "B"
  #   ...
  #   "Z"
  #   "AA"

Converting array of key value pairs to hash in Ruby

All you need to do is split each part of the array into a key and value (yielding an array of two-element arrays) and then pass the result to the handy Hash[] method:

arr = [ "Name = abc", "Id = 123", "Interest = Rock Climbing" ]

keys_values = arr.map {|item| item.split /\s*=\s*/ }
# => [ [ "Name", "abc" ],
#      [ "Id", "123" ],
#      [ "Interest", "Rock Climbing" ] ]

hsh = Hash[keys_values]
# => { "Name" => "abc",
#      "Id" => "123",
#      "Interest" => "Rock Climbing" }

Converting an array to hash in ruby

testarr = [["Actor", "Morgan", "33", ["A","B"]],
  ["Movie", "Titanic", "44", ["A","A"]],
  ["Actor", "Jack Black", "333", ["A","A"]]]

  a = Hash.new{ |h,k| h[k] = [] }

  testarr.each do |arr|
    b = {name: arr[1], age: arr[2], films: arr[3]}
    a[arr[0]] << b
  end

this will produce

{"Actor"=>[{"name"=>"Morgan", "age"=>"33", "films"=>["A", "B"]}, {"name"=>"Jack Black", "age"=>"333", "films"=>["A", "A"]}], "Movie"=>[{"name"=>"Titanic", "age"=>"44", "films"=>["A", "A"]}]}

Ruby array to hash: each element the key and derive value from it

Ruby's each_with_object method is a neat way of doing what you want

['a', 'b'].each_with_object({}) { |k, h| h[k] = k.upcase }

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