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](http://devblog.avdi.org/2010/08/02/using-and-and-or-in-ruby/). They are **not** the same. — Andrew Marshall, Mar 13 '12 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., Mar 13 '12 at 18:03

Victor Moroz · Answer 1 · 2012-03-13T21:12:50.873

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 '12 at 21:12

answered Mar 13 '12 at 17:55

Victor Moroz

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why `item.relationship_1` dosen't work on my ruby 1.9.2 install? I must make `item[:relationship_1]` to work. – Ismael Abreu Mar 13 '12 at 18:12

score 3 · Accepted Answer · edited Mar 13 '12 at 18:57

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 '12 at 18:57

Phrogz

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answered Mar 13 '12 at 17:55

Austin Taylor

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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. – Jeremy B. Mar 13 '12 at 18:04
1

[The implementation of `uniq_by`](https://github.com/rails/rails/blob/7194b393a611727fb36e8f586910e75db1bae746/activesupport/lib/active_support/core_ext/array/uniq_by.rb#L6) is (i think) actually rather clever and worthy of inspection. – Andrew Marshall Mar 13 '12 at 18:07
3

Nonsense, sort of. 1.9's [`Array#uniq`](http://ruby-doc.org/core-1.9.3/Array.html#method-i-uniq) can take a block and `Array#uniq` certainly is in the core. – mu is too short Mar 13 '12 at 18:08
@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](https://github.com/ruby/ruby/blob/trunk/array.c#L3608).) – Andrew Marshall Mar 13 '12 at 18:22
@muistooshort Good call. Didn't know that. – Austin Taylor Mar 13 '12 at 18:41
@AndrewMarshall (and Austin): To be fair, the documentation isn't exactly clear and explicit, nice to see that it is being fixed. – mu is too short Mar 14 '12 at 00:22

score 1 · Answer 3 · edited May 23 '17 at 11:56

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 '17 at 11:56

Community

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answered Mar 13 '12 at 18:01

Boris Strandjev

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Remove similar objects from array

3 Answers3