Groovy Goodness: New Methods to Sort and Remove Duplicates From Collection
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Join For FreeIn 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
andtoUnique
.
In the following sample we see the new methods in action:
@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.
Published at DZone with permission of Hubert Klein Ikkink, DZone MVB. See the original article here.
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