# Getting an array of unique objects of a class i wrote **URL:** \ **Category:** ruby-talk\ **Created:** [14 September 2008 11:08 UTC](https://rubytalk.org/t/getting-an-array-of-unique-objects-of-a-class-i-wrote/49076 "2008-09-14T11:08:09Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Adam\_Akhtar](https://avatars.discourse-cdn.com/v4/letter/a/c89c15/32.png) [@Adam\_Akhtar](https://rubytalk.org/u/Adam_Akhtar)\ **Post date:** [14 September 2008 11:08 UTC](https://rubytalk.org/t/getting-an-array-of-unique-objects-of-a-class-i-wrote/49076/1 "2008-09-14T11:08:09Z")
Hi Ive done some searching on this but couldnt find an answer that was either totally appropriate or one that i could understand ;\> (some advanced stuff going on). So if i have a class with two variables (strings) like this class thing attr\_accessor :name :job end and i want to ensure that if i have an array of these objects there will be no duplicates. A duplicate would be where both the name and job are the same in both objects. I tried using uniq! but it didnt work. Not sure why (can someone explain that). Ive heard of set, could that be used in this case to prevent duplicates being added? > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Lex\_Williams](https://avatars.discourse-cdn.com/v4/letter/l/e5b9ba/32.png) [@Lex\_Williams](https://rubytalk.org/u/Lex_Williams)\ **Post date:** [14 September 2008 11:14 UTC](https://rubytalk.org/t/getting-an-array-of-unique-objects-of-a-class-i-wrote/49076/2 "2008-09-14T11:14:41Z")
use a hash > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Michael\_Guterl1](https://avatars.discourse-cdn.com/v4/letter/m/e47c2d/32.png) [@Michael\_Guterl1](https://rubytalk.org/u/Michael_Guterl1)\ **Post date:** [14 September 2008 11:21 UTC](https://rubytalk.org/t/getting-an-array-of-unique-objects-of-a-class-i-wrote/49076/3 "2008-09-14T11:21:37Z")
You need to implement Thing#eql? and Thing#hash in order for a Array#uniq, Set, or Hash to function as you expect. > **···** > > On Sun, Sep 14, 2008 at 7:08 AM, Adam Akhtar \ wrote: > > > Hi Ive done some searching on this but couldnt find an answer that was > > either totally appropriate or one that i could understand ;\> (some > > advanced stuff going on). > > > > So if i have a class with two variables (strings) like this > > > > class thing > > attr\_accessor :name :job > > end > > > > and i want to ensure that if i have an array of these objects there will > > be no duplicates. A duplicate would be where both the name and job are > > the same in both objects. > > > > I tried using uniq! but it didnt work. Not sure why (can someone explain > > that). > > > > Ive heard of set, could that be used in this case to prevent duplicates > > being added? ---
**Author:** ![Sebastian\_Hungereck1](https://avatars.discourse-cdn.com/v4/letter/s/3ab097/32.png) [@Sebastian\_Hungereck1](https://rubytalk.org/u/Sebastian_Hungereck1)\ **Post date:** [14 September 2008 11:29 UTC](https://rubytalk.org/t/getting-an-array-of-unique-objects-of-a-class-i-wrote/49076/4 "2008-09-14T11:29:37Z")
Adam Akhtar wrote: > class thing > attr\_accessor :name :job > end Thing = Struct.new(:name, :job) > and i want to ensure that if i have an array of these objects there will > be no duplicates. A duplicate would be where both the name and job are > the same in both objects. > > I tried using uniq! but it didnt work. Not sure why (can someone explain > that). For uniq to work your class has to implement hash and eql?, so that for any two objects that you consider equal o1.hash == o2.hash and o1.eql?(o2) and for any two objects that you do not consider equal !o1.eql?(o2) (o1.hash may still be equal to o2.hash, but should not be). > Ive heard of set, could that be used in this case to prevent duplicates > being added? If uniq does not work, set does not work either. Once you implement hash and eql?, yes, set can be used. If you use Struct to define your class, like I demonstrated above hash and eql? will be defined automatically. If you can't use a struct, you could define them as such: class Thing   attr\_accessor :name, :job   def hash     [name, job].hash   end   def eql?(other)     [name, job].eql?([other.name, other.job])   end end HTH, Sebastian > **···** > > -- > NP: Die Apokalyptischen Reiter - Heut' Ist Der Tag > Jabber: sepp2k@jabber.org > ICQ: 205544826 ---
**Author:** ![Adam\_Akhtar](https://avatars.discourse-cdn.com/v4/letter/a/c89c15/32.png) [@Adam\_Akhtar](https://rubytalk.org/u/Adam_Akhtar)\ **Post date:** [16 September 2008 09:59 UTC](https://rubytalk.org/t/getting-an-array-of-unique-objects-of-a-class-i-wrote/49076/5 "2008-09-16T09:59:35Z")
Thank you everyone for your reply. Ive implemented the hash and eql? definitions for my class and it worked. On a similiar note what do i have to do for my unit tests which compare two objects to work. I.e. assert\_equal(expected\_object, some\_method\_which\_returns\_an\_object()) where both the compared objects are instances of a class i defined. So far my unit tests fail despite the variables within the objects being identical. the only difference is the object\_id which i guess is important. I impleted hash and eql? like above but the tests still dont pass. > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Brian\_Candler](https://avatars.discourse-cdn.com/v4/letter/b/5f9b8f/32.png) [@Brian\_Candler](https://rubytalk.org/u/Brian_Candler)\ **Post date:** [16 September 2008 11:49 UTC](https://rubytalk.org/t/getting-an-array-of-unique-objects-of-a-class-i-wrote/49076/6 "2008-09-16T11:49:11Z")
Adam Akhtar wrote: > Thank you everyone for your reply. Ive implemented the hash and eql? > definitions for my class and it worked. On a similiar note what do i > have to do for my unit tests which compare two objects to work. > > I.e. > > assert\_equal(expected\_object, some\_method\_which\_returns\_an\_object()) Look at the source for assert\_equal 🙂 /usr/lib/ruby/1.8/test/unit/assertions.rb       def assert\_equal(expected, actual, message=nil) ...         assert\_block(full\_message) { expected == actual } So your object needs to implement '==' too. > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).