Trouble sorting records on unique attributes..

Question

Working with the following code, I need to return only records where the `point' attribute is unique. I can't seem to get there by myself.

uniques = Item.find_all_by_item_id(item_id)
uniques.sort! {|a, b| b.point <=> a.point } # how do I reject the equal points?

In other words.. I guess, how do you make [0, 1, 1, 1, 2, 3, 3, 4, 4, 7] #=> [0, 2, 7] ?

Answer 1

How about this:

# Get the number of items with each point value
counts = Item.count("point", :group => "point")

# Get the IDs of all entries that only show up once
unique_ids = counts.collect { |count| count[0] if count[1] == 1 }.compact

unique_items = Item.find_all_by_id(unique_ids)

Answer 2

I can think of few ways off the top of my head to do this:

uniques.reject!{|u| uniques.select{|x| x == u}.size > 1}

Basically iterate through the uniques array and then see if there is more than one of those items in the array. Obviously there are lots of clever ways to speed this up, but for small arrays this should work.

or

h = Hash.new(0)
uniques.each{|u| h[u] += 1}
h.reject{|k,v| v > 1}.keys

Basically count how many times each item shows up in a hash, if its more than one reject it and then just look at the keys.