Groovy Goodness: New Methods to Sort and Remove Duplicates From Collection

In Groovy we can use the sort and unique methods to sort a collection or remove duplicates from a collection. These methods alter the collection on which they are invoked. This is a side effect we might want to avoid. Therefore the sort and unique methods where changed and we could pass a boolean argument to indicate if the original collection should be changed or that we must have a new collection as the result of the methods, leaving the original collection untouched. Since Groovy 2.4 we have two new methods which by default return a new collection: toSorted and toUnique.

In the following sample we see the new methods in action:

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@groovy.transform.Sortable @groovy.transform.ToString class User {     String username, email }   def mrhaki1 = new User(username: 'mrhaki', email: 'mrhaki@localhost') def mrhaki2 = new User(username: 'mrhaki', email: 'user@localhost') def hubert1 = new User(username: 'hubert', email: 'user@localhost') def hubert2 = new User(username: 'hubert', email: 'hubert@localhost')     // We make the list immutable, // so we check the toSorted and toUnique methods // do not alter it. def users = [mrhaki1, mrhaki2, hubert1, hubert2].asImmutable()     // toSorted def sortedUsers = users.toSorted()   // @Sortable adds a compareTo method // to User class to sort first by username // and then email. assert sortedUsers == [hubert2, hubert1, mrhaki1, mrhaki2]   // Original list is unchanged. assert users == [mrhaki1, mrhaki2, hubert1, hubert2]   // Use toSorted with closure. def sortedByEmail = users.toSorted { a, b -> a.email <=> b.email } assert sortedByEmail == [hubert2, mrhaki1, mrhaki2, hubert1]   // Or use toSorted with Comparator. // @Sortable added static comparatorByProperty // methods. def sortedByEmailComparator = users.toSorted(User.comparatorByEmail()) assert sortedByEmailComparator == [hubert2, mrhaki1, mrhaki2, hubert1]     // toUnique with Comparator. def uniqueUsers = users.toUnique(User.comparatorByUsername()) assert uniqueUsers == [mrhaki1, hubert1] assert users == [mrhaki1, mrhaki2, hubert1, hubert2]   // toUnique with Closure. def uniqueByEmail = users.toUnique { a, b -> a.email <=> b.email } assert uniqueByEmail == [mrhaki1, mrhaki2, hubert2]

Written with Groovy 2.4.3.