Ruby, unique hashes in array based on multiple fields

Question

I'd like to get back an array of hashes based on sport and type combination

I've got the following array:

[
    { sport: "football", type: 11, other_key: 5 }, 
    { sport: "football", type: 12, othey_key: 100  },
    { sport: "football", type: 11, othey_key: 700  },
    { sport: "basketball", type: 11, othey_key: 200 },
    { sport: "basketball", type: 11, othey_key: 500 }
]

I'd like to get back:

[
    { sport: "football", type: 11, other_key: 5 }, 
    { sport: "football", type: 12, othey_key: 100  },
    { sport: "basketball", type: 11, othey_key: 200 },
]

I tried to use (pseudocode):

[{}, {}, {}].uniq { |m| m.sport and m.type }

I know I can create such array with loops, I'm quite new to ruby and I'm curious if there's a better (more elegant) way to do it.

Yes, uniq with a block is the way to go, but here's another way: arr.group_by { |h| [h[:sport],h[:type]] }.values.map(&:first). — Cary Swoveland
– Cary Swoveland, Commented Sep 19, 2014 at 1:15

Kyle · Accepted Answer · 2014-09-18 18:52:41Z

24

Try using Array#values_at to generate an array to uniq by.

sports.uniq{ |s| s.values_at(:sport, :type) }

answered Sep 18, 2014 at 18:52

Kyle

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1 Comment

Tim Dorr Over a year ago

Just a tiny correction: uniq is passing in each value to the block, so that's actually a Hash in this case and it would be calling Hash#values_at. Just be careful if you have an array of things other than hashes or arrays.

Kyle · Accepted Answer · 2014-09-18 19:17:08Z

7

One solution is to build some sort of key with the sport and type, like so:

arr.uniq{ |m| "#{m[:sport]}-#{m[:type]}" }

The way uniq works is that it uses the return value of the block to compare elements.

edited Sep 18, 2014 at 19:17

Kyle

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answered Sep 18, 2014 at 18:50

mbillard

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Comments

7stud · Accepted Answer · 2014-09-18 18:53:43Z

4

require 'pp'

data = [
    { sport: "football", type: 11, other_key: 5 }, 
    { sport: "football", type: 12, othey_key: 100  },
    { sport: "football", type: 11, othey_key: 700  },
    { sport: "basketball", type: 11, othey_key: 200 },
    { sport: "basketball", type: 11, othey_key: 500 }
]

results = data.uniq do |hash|
  [hash[:sport], hash[:type]]
end

pp results

--output:--
[{:sport=>"football", :type=>11, :other_key=>5},
 {:sport=>"football", :type=>12, :othey_key=>100},
 {:sport=>"basketball", :type=>11, :othey_key=>200}]

answered Sep 18, 2014 at 18:53

7stud

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