Remove similar objects from array

Question

I have an array of hashes:

[{ item_id: 1, relationship_1: 1, relationship_2: 1, value: 'go' },
 { item_id: 2, relationship_1: 2, relationship_2: 2, value: 'stop' },
 { item_id: 3, relationship_1: 2, relationship_2: 1, value: 'stop' }, #remove
 { item_id: 4, relationship_1: 3, relationship_2: 1, value: 'go' },
 { item_id: 5, relationship_1: 1, relationship_2: 2, value: 'go' }] #remove

I want the lines commented to be removed. The need is to remove all lines that have relationship_1 and value in common. The only way I can think of is:

items.each do |i|
  items.each do |k|
    if i.item_id != k.item_id and i.relationship_1 == k.relationship_1 and i.value == k.value
      items.remove(k)
    end
  end
end

This is not working as intended. What is the most "Ruby" way to remove those offending items?

How do you define "similar"? Also please read about the difference between &&/|| & and/or in Ruby. They are not the same. — Andrew Marshall
– Andrew Marshall, Commented Mar 13, 2012 at 17:52
In this case I mean by having a specific set of values that are equal, there wasn't really a better way to word it in the title. — Jeremy B.
– Jeremy B., Commented Mar 13, 2012 at 18:03

Phrogz · Accepted Answer · 2012-03-13 18:57:44Z

3

Unfortunately, uniq_by isn't available in Ruby core. Pull it in with require 'activesupport'.

items.uniq_by {|h| [h[:replationship_1], h[:value]] }

Edit: As noted by @mu below, Ruby 1.9's uniq also works:

items.uniq{|h| [h[:replationship_1], h[:value]] }

edited Mar 13, 2012 at 18:57

Phrogz

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answered Mar 13, 2012 at 17:55

Austin Taylor

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6 Comments

Jeremy B. Over a year ago

Fortunately I am using Rails 3. I didn't want extra requirements if it didn't need them. Seeing as these objects are ActiveResource objects, this will work great. Thank you.

Andrew Marshall Over a year ago

The implementation of uniq_by is (i think) actually rather clever and worthy of inspection.

mu is too short Over a year ago

Nonsense, sort of. 1.9's Array#uniq can take a block and Array#uniq certainly is in the core.

Andrew Marshall Over a year ago

@muistooshort I thought it did, but I was surprised when I looked at the docs and the method's signature doesn't state it takes a block so I didn't even bother to look at the examples. (Thankfully this doc issue is fixed in Ruby trunk.)

Austin Taylor Over a year ago

@muistooshort Good call. Didn't know that.

|

Victor Moroz · Accepted Answer · 2012-03-13 21:12:50Z

3

group_by{ |item| [item.relationship_1, item.value] }.values.map(&:first)?

UPDATE

Oops, it was a hash:

group_by{ |item| [item[:relationship_1], item[:value]] }.values.map(&:first)

or

group_by{ |item| item.values_at(:relationship_1, :value) }.values.map(&:first)

edited Mar 13, 2012 at 21:12

answered Mar 13, 2012 at 17:55

Victor Moroz

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1 Comment

Ismael Over a year ago

why item.relationship_1 dosen't work on my ruby 1.9.2 install? I must make item[:relationship_1] to work.

Community · Accepted Answer · 2017-05-23 11:56:25Z

1

Maybe this function will help. I found it mentioned in this thread, and if I am not wrong it is part of latest ruby on rails.

a.uniq_by {|t| [t.replationship_1, t.value]}

edited May 23, 2017 at 11:56

CommunityBot

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answered Mar 13, 2012 at 18:01

Boris Strandjev

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