stackoverflow の answer にある
Items.all.to_a.uniq { |item| item.name }
の方法では目的にあわなかったのでしょうか?
この方法の場合は次のようにしました。(質問文のものとは異なる列名、値ですが)
↓は rails c での実行例です。
[8] pry(main)> Order.all
Order Load (0.3ms) SELECT "orders".* FROM "orders" ORDER BY ordered_at DESC
+----+-----------+----------+-------+-------------------------+-------------------------+-------------------------+
| id | client_id | status | price | ordered_at | created_at | updated_at |
+----+-----------+----------+-------+-------------------------+-------------------------+-------------------------+
| 2 | 1 | active | 200 | 2000-01-01 04:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
| 5 | 2 | payed | 210 | 2000-01-01 04:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
| 1 | 1 | received | 100 | 2000-01-01 09:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
| 3 | 1 | payed | 400 | 2000-01-01 09:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
| 4 | 2 | payed | 110 | 2000-01-01 09:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
| 6 | 2 | payed | 410 | 2000-01-01 09:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
+----+-----------+----------+-------+-------------------------+-------------------------+-------------------------+
6 rows in set
[9] pry(main)> Order.all.to_a.uniq { |item| item.status }
Order Load (0.2ms) SELECT "orders".* FROM "orders" ORDER BY ordered_at DESC
+----+-----------+----------+-------+-------------------------+-------------------------+-------------------------+
| id | client_id | status | price | ordered_at | created_at | updated_at |
+----+-----------+----------+-------+-------------------------+-------------------------+-------------------------+
| 2 | 1 | active | 200 | 2000-01-01 04:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
| 5 | 2 | payed | 210 | 2000-01-01 04:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
| 1 | 1 | received | 100 | 2000-01-01 09:58:33 UTC | 2016-03-12 09:58:33 UTC | 2016-03-12 09:58:33 UTC |
+----+-----------+----------+-------+-------------------------+-------------------------+-------------------------+
3 rows in set