How to check for uniqueness in an array of hashes

Question

I have an array of hashes where each hash contains a handful of keys. I want to check to see if any number of the hashes have the same user_id.

An example would look like this:

[ {:id => 1, :user_id => 2, :location => nil, :facility_id => nil}
  {:id => 3, :user_id => 2, :location => 'China', :facility_id => 20} ]

I would need this to return true in this case, where two of the hashes have a user_id in common. How do I do this the 'ruby way'?

steenslag · Accepted Answer · 2012-10-03 18:40:52Z

4

arr = [ {:id => 1, :user_id => 2, :location => nil, :facility_id => nil},
  {:id => 3, :user_id => 2, :location => 'China', :facility_id => 20} ]
p arr != arr.uniq{|u| u[:user_id]} #=> true

answered Oct 3, 2012 at 18:40

steenslag

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3 Comments

Ivaylo Strandjev Over a year ago

My idea was almost the same but one note - comparing the sizes should be enough. Comparing the whole arrays will be slower.

steenslag Over a year ago

@izomorphius Ruby seems to optimize for this (line 1463). But generally speaking, you are right.

Ivaylo Strandjev Over a year ago

this optimization works only for the false case. Imagine you have an array with 10 hashes with different user_id-s and each hash has a size of hundreds of megabytes.

Ivaylo Strandjev · Accepted Answer · 2012-10-03 18:41:52Z

3

Try this:

a.map{|t| t[:user_id]}.uniq.size == a.size

answered Oct 3, 2012 at 18:41

Ivaylo Strandjev

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