how to group objects in an array Ruby

Question

I have an array of users who are managers.

However there are repeated Users.

I would like to group them so that there is only one instance of each User in the array.

What would be the best way to go about this?

@managers.sort_by{|obj| obj.id} # Just sorted the data but did not eliminate duplicats
@managers.group_by{|u|u.name} # just created a bunch of arrays for each name

• chell: Thanks to everyone for giving me such great answers. Really helps a NOOB learn this stuff.

Answer 1

Use the uniq method, which returns a new array with duplicates removed.

@managers.uniq

• m_x: or @managers.uniq_by {|manager| manager.user_id} (see apidock.com/rails/Array/uniq_by)

Answer 2

If by duplicate you mean the same object ID, then you can do the following:

@managers.uniq.group_by(&:name)

Answer 3

Filtering the array feels like fixing symptoms. Why does the array contain rubbish in the first place?

I would suggest adding a manager? method to your User model that returns true if the user is a manager. Then you could to something like

@managers = User.select &:manager?

and get an array that only contains managers.

• m_x: i agree with you that this looks symptomatic, but does this not lead straight to a N+1 query problem if your manager? method tries to find records associated to each user ? (unless using a "manager" column set to true/false by a callback when applying to a manager job/quiting)
• Simon Ernst: I had a role column in mind, with the manager? method returning true if the the user had the matching role. But you are right in your scenario. I guess we don't know enough about the context given here.
• chell: In my case the way it works is the same person can be the manager of many boards they create. So over time I would get more than one board possibly by the same manager.

Answer 4

you can also do

Manager.select('DISTINCT user_id')

to get a clean array in the first place, whith better performance.