filter array of hashes with an array of keys ruby

Question

arr = [
  {
    :id=>2,
    :start=> "3:30",
    break: 30,
    num_attendees: 14
  },
  {
    id: 3,
    start: "3: 40",
    break: 40,
    num_attendees: 4
  },
  {
    id: 4,
    start: "4: 40",
    break: 10,
    num_attendees: 40
  }
]

When I do the following

arr.map do |hash|
 [ hash[:id], hash[:start] ]
end

returns

#=> [[2, "3:30"], [3, "3: 40"], [4, "4: 40"]]

Is there an elegant and efficient way of passing an array like return_keys = [:id, :start] and get the same above values rather than hard coding inside the array.map

spickermann · Accepted Answer · 2020-04-22 19:27:16Z

1

Would you consider the following elegant and efficient?

arr.map { |h| h.values_at(:id, :start) }
#=> [[2, "3:30"], [3, "3: 40"], [4, "4: 40"]]

or

arr.map { |h| h.values_at(*return_keys) }
#=> [[2, "3:30"], [3, "3: 40"], [4, "4: 40"]]

answered Apr 22, 2020 at 19:27

spickermann

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1 Comment

Sri Over a year ago

It is elegant for sure but I have not benchmarking with anything else. So Thank you!

xplosiveFibonacci · Accepted Answer · 2020-04-22 20:32:47Z

1

I find the following really expressive

keys = [:id, :start]
arr.map {|hash| hash.slice(*keys).values}

The slice method returns a hash only with the keys passed as parameters (which are preceded by the * operator to convert an array into keyword arguments and avoid hardcoding). Then, the values method gets just the values out of the hash

answered Apr 22, 2020 at 20:32

xplosiveFibonacci

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