Rails 3 - How to sort an array by number of duplicates

Question

Sorry for the noob question (i guess...).

Say I have an array of post_commenters with user_id & comment_id
E.g.:
1 - 27
2 - 31
1 - 54
3 - 87
1 - 12
2 - 54

If I wanted to rank the users by their number of comments, I'd have to count the number of times they have commented, and then .uniq it.

How can I do that ?

I know how to uniq it:

unique_user_list = array.uniq {|s| s.user_id}

I know how to count the duplicates inside the array:

array.count { |u| u.name == unique_user_list.name  } # in a loop of user

But i'm at a loss to mix and sort by number of duplicates...
Thank you!

EDIT

Ok, thanks to floatless, i'm now at something more tangible - with a real example from the foursquare api, using quimby gem:

- current_user.all_checkins.group_by(&:venue["id"]).first(50).each do |c|
  = c.venue.id

Only problem, it doesn't .... group.
Any idea?

Daniel O'Hara · Accepted Answer · 2011-05-25 19:20:29Z

1

I think you should use a GROUP BY clause inside your SQL query to do that and then just COUNT grouped comments.

answered May 25, 2011 at 19:20

Daniel O'Hara

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1 Comment

My example was a dummy example - i'm getting an array from an api, don't think the group_by works here...