We can easily remove duplicate elements in a collection with the different unique() methods. Without any parameters the default comparator for the objects is used to determine duplicate elements. But we can also use a closure to define the rules for duplicate elements. The closure can have one parameter and then we must return a value that is used for comparison, or the closure has two parameters and then we must return an Integer value where 0 means the items are not unique. Finally we can pass our own Comparator implementation to the unique() method where we define when an element is unique or not.
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class User implements Comparable {
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String username, email
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boolean active
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int compareTo(Object other) {
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username <=> other.username
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}
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}
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def mrhaki1 = new User(username: 'mrhaki', email: 'mrhaki@localhost', active: false)
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def mrhaki2 = new User(username: 'mrhaki', email: 'user@localhost', active: true)
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def hubert1 = new User(username: 'hubert', email: 'user@localhost', active: false)
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def hubert2 = new User(username: 'hubert', email: 'hubert@localhost', active: true)
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// Caution: unique() changes the original collection, so
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// for the sample we invoke unique each time on a fresh new
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// user list.
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def uniqueUsers = [mrhaki1, mrhaki2, hubert1, hubert2].unique()
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assert 2 == uniqueUsers.size()
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assert [mrhaki1, hubert1] == uniqueUsers
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// Use closure with one parameter.
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def uniqueEmail = [mrhaki1, mrhaki2, hubert1, hubert2].unique { user ->
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user.email
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}
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assert 3 == uniqueEmail.size()
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assert [mrhaki1, mrhaki2, hubert2] == uniqueEmail
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// Use closure with two parameters.
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def uniqueActive = [mrhaki1, mrhaki2, hubert1, hubert2].unique { user1, user2 ->
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user1.active <=> user2.active
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}
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assert 2 == uniqueActive.size()
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assert [mrhaki1, mrhaki2] == uniqueActive
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// Use a comparator.
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def emailComparator = [
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equals: { delegate.equals(it) },
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compare: { first, second ->
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first.email <=> second.email
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}
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] as Comparator
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def unique = [mrhaki1, mrhaki2, hubert1, hubert2].unique(emailComparator)
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assert 3 == unique.size()
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assert [mrhaki1, mrhaki2, hubert2] == unique