How do I get unique attribute values of an array of objects?

Question

I'm using RoR 5. How do I select unique attribute values from an array of objects? I've tried

attr_values = my_objects.uniq{|r| r.attr_name}

But "attr_values" is an array of objects of the same type that "my_objects" consists of. I want the array to be objects of the type of "r.attr_name."

Can you give an example of the input and expected output? If this is a collection of records from the database you can use .distinct or grouping instead which avoids loading a huge amount of records from the DB. — max
– max, Commented Oct 5, 2017 at 14:29
@bkunzi01 using my_objects.pluck('DISTINCT attr_name') could be better than pulling all the data out in the first place. — max
– max, Commented Oct 5, 2017 at 14:32
I'm guessing attr_values = my_objects.map(&:attr_name).uniq is what he is looking for but its a really fuzzy question. @SergioTulentsev — max
– max, Commented Oct 5, 2017 at 14:37
Read the comments too late, but @max has it right. You can combine .distinct and .pluck without the SQL segment, see my answer. @bkunzi01, your solution creates a big array, only to remove duplicates later, it won't be performant. — Leonel Galán
– Leonel Galán, Commented Oct 5, 2017 at 16:18

Leonel Galán · Accepted Answer · 2017-10-05 16:15:58Z

2

It's not clear on your post, but if that "array" is instead an ActiveRecord::Relation, you could do .distinct.pluck(:attr_name), for example: User.distinct.pluck(:role) => SELECT DISTINCT "users"."role" FROM "users"

If it's actually an array (my_objects.is_a? Array), the solution is my_objects.map(&:attr_name).uniq.

answered Oct 5, 2017 at 16:15

Leonel Galán

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