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rubyarraysperformancehash

Convert array-of-hashes to a hash-of-hashes, indexed by an attribute of the hashes

I've got an array of hashes representing objects as a response to an API call. I need to pull data from some of the hashes, and one particular key serves as an id for the hash object. I would like to convert the array into a hash with the keys as the ids, and the values as the original hash with that id.

Here's what I'm talking about:

api_response = [
  { :id => 1, :foo => 'bar' },
  { :id => 2, :foo => 'another bar' },
  # ..
]

ideal_response = {
  1 => { :id => 1, :foo => 'bar' },
  2 => { :id => 2, :foo => 'another bar' },
  # ..
}

There are two ways I could think of doing this.

  1. Map the data to the ideal_response (below)
  2. Use api_response.find { |x| x[:id] == i } for each record I need to access.
  3. A method I'm unaware of, possibly involving a way of using map to build a hash, natively.

My method of mapping: 

keys = data.map { |x| x[:id] }
mapped = Hash[*keys.zip(data).flatten]

I can't help but feel like there is a more performant, tidier way of doing this. Option 2 is very performant when there are a very minimal number of records that need to be accessed. Mapping excels here, but it starts to break down when there are a lot of records in the response. Thankfully, I don't expect there to be more than 50-100 records, so mapping is sufficient.

Is there a smarter, tidier, or more performant way of doing this in Ruby?

Solution

  • Ruby <= 2.0

    > Hash[api_response.map { |r| [r[:id], r] }]
#=> {1=>{:id=>1, :foo=>"bar"}, 2=>{:id=>2, :foo=>"another bar"}}

    However, Hash::[] is pretty ugly and breaks the usual left-to-right OOP flow. That's why Facets proposed Enumerable#mash:

    > require 'facets'
> api_response.mash { |r| [r[:id], r] }
#=> {1=>{:id=>1, :foo=>"bar"}, 2=>{:id=>2, :foo=>"another bar"}}

    This basic abstraction (convert enumerables to hashes) was asked to be included in Ruby long ago, alas, without luck.

    Note that your use case is covered by Active Support: Enumerable#index_by

    Ruby >= 2.1

    [UPDATE] Still no love for Enumerable#mash, but now we have Array#to_h. It creates an intermediate array, but it's better than nothing:

    > object = api_response.map { |r| [r[:id], r] }.to_h