collectNested ( Closure transform) Recursively iterates through this collection transforming each non-Collection value into a new value using the closure as a transformer. Iterates through a Collection, passing each item and the item's index (a counter starting at zero) to the given closure. grep ( Object filter) Iterates over the collection of items and returns each item that matches the given filter - calling the Object#isCase(java.lang.Object) method used by switch statements. method can be used with different kinds of filters like regular expressions, classes, ranges etc. inject ( Closure closure) Performs the same function as the version of inject that takes an initial value, but uses the head of the Collection as the initial value, and iterates over the tail. inject ( Object initialValue, Closure closure) Iterates through the given Collection, passing in the initial value to the 2-arg closure along with the first item. isCase ( Object switchValue) 'Case' implementation for collections which tests if the 'switch' operand is contained in any of the 'case' values. leftShift ( Object value) Overloads the left shift operator to provide an easy way to append objects to a Collection. minus ( Collection removeMe) Create a new Collection composed of the elements of the first Collection minus every occurrence of elements of the given Collection. removeAll ( Closure condition) Modifies this collection by removing the elements that are matched according to the specified closure condition. removeAll ( Object[] items) Modifies this collection by removing its elements that are contained within the specified object array. removeElement ( Object o) Modifies this collection by removing a single instance of the specified element from this collection, if it is present. retainAll ( Closure condition) Modifies this collection so that it retains only its elements that are matched according to the specified closure condition. retainAll ( Object[] items) Modifies this collection so that it retains only its elements that are contained in the specified array. unique ( Closure closure) A convenience method for making a collection unique using a Closure to determine duplicate (equal) items.

Methods inherited from interface java.lang. Iterable

any , asCollection , asList , asType , average , average , bufferedIterator , chop , collate , collate , collate , collate , collect , collect , collect , collectEntries , collectEntries , collectEntries , collectEntries , collectMany , collectMany , collectNested , collectNested , combinations , combinations , contains , containsAll , count , count , count , countBy , disjoint , drop , dropRight , dropWhile , each , eachCombination , eachPermutation , eachWithIndex , every , findIndexOf , findIndexOf , findIndexValues , findIndexValues , findLastIndexOf , findLastIndexOf , findResult , findResult , findResult , findResult , findResults , findResults , first , flatten , flatten , getAt , groupBy , groupBy , groupBy , head , indexed , indexed , init , inits , intersect , intersect , intersect , isEmpty , join , last , max , max , max , min , min , min , minus , minus , minus , minus , multiply , permutations , permutations , plus , plus , size , sort , sort , sort , sort , sort , stream , sum , sum , sum , sum , tail , tails , take , takeRight , takeWhile , toList , toSet , toSorted , toSorted , toSorted , toSpreadMap , toUnique , toUnique , toUnique , withIndex , withIndex

public boolean addAll ( Object[] items)

Modifies the collection by adding all the elements in the specified array to the collection. The behavior of this operation is undefined if the specified array is modified while the operation is in progress. See also plus or the '+' operator if wanting to produce a new collection containing additional items but while leaving the original collection unchanged.

Parameters:

items - array containing elements to be added to this collection

Coerce a collection instance to a boolean value. A collection is coerced to false if it's empty, and to true otherwise.

assert [1,2].asBoolean() == true

assert [].asBoolean() == false

public Object asType ( Class clazz)

Converts the given collection to another type. A default concrete type is used for List, Set, or SortedSet. If the given type has a constructor taking a collection, that is used. Otherwise, the call is deferred to Object#asType(Class). If this collection is already of the given type, the same instance is returned.

Parameters:

clazz - the desired class

public List collectNested ( Closure transform)

Recursively iterates through this collection transforming each non-Collection value into a new value using the closure as a transformer. Returns a potentially nested list of transformed values. assert [2,[4,6],[8],[]] == [1,[2,3],[4],[]].collectNested { it * 2 }

Iterates through a Collection, passing each item and the item's index (a counter starting at zero) to the given closure.

Parameters:

closure - a Closure to operate on each item

public Object find ()

Finds the first item matching the IDENTITY Closure (i.e. matching Groovy truth). Example: def items = [null, 0, 0.0, false, '', [], 42, 43] assert items.find() == 42

public Object find ( Closure closure)

Finds the first value matching the closure condition. Example:

def list = [1,2,3]
assert 2 == list.find { it > 1 }
                                    
public Collection findAll()
                                    
Finds the items matching the IDENTITY Closure (i.e. matching Groovy truth).
Example:
def items = [1, 2, 0, false, true, '', 'foo', [], [4, 5], null]
assert items.findAll() == [1, 2, true, 'foo', [4, 5]]
                                    
public Collection findAll(Closure closure)
                                    
Finds all values matching the closure condition.
assert [2,4] == [1,2,3,4].findAll { it % 2 == 0 }
                                        
Parameters:
                                        
closure -  a closure condition
                                    
public Collection flatten()
                                    
Flatten a Collection. This Collection and any nested arrays or
collections have their contents (recursively) added to the new collection.
assert [1,2,3,4,5] == [1,[2,3],[[4]],[],5].flatten()
                                    
public Collection grep()
                                    
Iterates over the collection returning each element that matches
using the IDENTITY Closure as a filter - effectively returning all elements which satisfy Groovy truth.
Example:
def items = [1, 2, 0, false, true, '', 'foo', [], [4, 5], null]
assert items.grep() == [1, 2, true, 'foo', [4, 5]]
                                    
public Collection grep(Object filter)
                                    
Iterates over the collection of items and returns each item that matches
the given filter - calling the Object#isCase(java.lang.Object)
method used by switch statements. method can be used with different
kinds of filters like regular expressions, classes, ranges etc.
Example:
def list = ['a', 'b', 'aa', 'bc', 3, 4.5]
assert list.grep( ~/a+/ )  == ['a', 'aa']
assert list.grep( ~/../ )  == ['aa', 'bc']
assert list.grep( Number ) == [ 3, 4.5 ]
assert list.grep{ it.toString().size() == 1 } == [ 'a', 'b', 3 ]
                                    
public Object inject(Closure closure)
                                    
Performs the same function as the version of inject that takes an initial value, but
uses the head of the Collection as the initial value, and iterates over the tail.
assert 1 * 2 * 3 * 4 == [ 1, 2, 3, 4 ].inject { acc, val -> acc * val }
assert ['b'] == [['a','b'], ['b','c'], ['d','b']].inject { acc, val -> acc.intersect( val ) }
LinkedHashSet set = [ 't', 'i', 'm' ]
assert 'tim' == set.inject { a, b -> a + b }
                                    
public Object inject(Object initialValue, Closure closure)
                                    
Iterates through the given Collection, passing in the initial value to
the 2-arg closure along with the first item. The result is passed back (injected) into
the closure along with the second item. The new result is injected back into
the closure along with the third item and so on until the entire collection
has been used. Also known as foldLeft or reduce in functional parlance.
Examples:
assert 1*1*2*3*4 == [1,2,3,4].inject(1) { acc, val -> acc * val }
assert 0+1+2+3+4 == [1,2,3,4].inject(0) { acc, val -> acc + val }
assert 'The quick brown fox' ==
    ['quick', 'brown', 'fox'].inject('The') { acc, val -> acc + ' ' + val }
assert 'bat' ==
    ['rat', 'bat', 'cat'].inject('zzz') { min, next -> next < min ? next : min }
def max = { a, b -> [a, b].max() }
def animals = ['bat', 'rat', 'cat']
assert 'rat' == animals.inject('aaa', max)
Visual representation of the last example above:
   initVal  animals[0]
      v        v
max('aaa',   'bat')  =>  'bat'  animals[1]
                           v       v
                     max('bat',  'rat')  =>  'rat'  animals[2]
                                               v       v
                                         max('rat',  'cat')  =>  'rat'
                                    
public Collection intersect(Collection right)
                                    
Create a Collection composed of the intersection of both collections.  Any
elements that exist in both collections are added to the resultant collection.
For collections of custom objects; the objects should implement java.lang.Comparable
assert [4,5] == [1,2,3,4,5].intersect([4,5,6,7,8])
By default, Groovy uses a NumberAwareComparator when determining if an
element exists in both collections.
                                        
Parameters:
                                        
right -  a Collection
                                    
public Collection intersect(Collection right, Comparator comparator)
                                    
Create a Collection composed of the intersection of both collections.  Any
elements that exist in both collections are added to the resultant collection.
For collections of custom objects; the objects should implement java.lang.Comparable
assert [3,4] == [1,2,3,4].intersect([3,4,5,6], Comparator.naturalOrder())
assert [2,4] == [1,2,3,4].intersect([4,8,12,16,20], (x, y) -> x * x <=> y)
def one = ['a', 'B', 'c', 'd']
def two = ['b', 'C', 'd', 'e']
def compareIgnoreCase = { a, b -> a.toLowerCase() <=> b.toLowerCase() }
assert one.intersect(two) == ['d']
assert two.intersect(one) == ['d']
assert one.intersect(two, compareIgnoreCase) == ['B', 'c', 'd']
assert two.intersect(one, compareIgnoreCase) == ['b', 'C', 'd']
                                    
public boolean isCase(Object switchValue)
                                    
'Case' implementation for collections which tests if the 'switch'
operand is contained in any of the 'case' values.
For example:
switch( 3 ) {
  case [1,3,5]:
    assert true
    break
  default:
    assert false
                                        
Parameters:
                                        
switchValue -  the switch value
                                    
public Collection leftShift(Object value)
                                    
Overloads the left shift operator to provide an easy way to append
objects to a Collection.
def list = [1,2]
list << 3
assert list == [1,2,3]
                                        
Parameters:
                                        
value -  an Object to be added to the collection.
                                    
public Collection minus(Collection removeMe)
                                    
Create a new Collection composed of the elements of the first Collection minus
every occurrence of elements of the given Collection.
assert [1, "a", true, true, false, 5.3] - [true, 5.3] == [1, "a", false]
                                        
Parameters:
                                        
removeMe -  a Collection of elements to remove
                                    
public Collection plus(Iterable right)
                                    
Create a Collection as a union of a Collection and an Iterable. If the left collection
is a Set, then the returned collection will be a Set otherwise a List.
This operation will always create a new object for the result,
while the operands remain unchanged.
                                        
Parameters:
                                        
right -  the right Iterable
                                    
public Collection plus(Object right)
                                    
Create a collection as a union of a Collection and an Object. If the collection
is a Set, then the returned collection will be a Set otherwise a List.
This operation will always create a new object for the result,
while the operands remain unchanged.
assert [1,2,3] == [1,2] + 3
                                        
Parameters:
                                        
right -  an object to add/append
                                    
public Collection plus(Collection right)
                                    
Create a Collection as a union of two collections. If the left collection
is a Set, then the returned collection will be a Set otherwise a List.
This operation will always create a new object for the result,
while the operands remain unchanged.
assert [1,2,3,4] == [1,2] + [3,4]
                                        
Parameters:
                                        
right -  the right Collection
                                    
public boolean removeAll(Closure condition)
                                    
Modifies this collection by removing the elements that are matched according
to the specified closure condition.
def list = ['a', 'b']
list.removeAll { it == 'b' }
assert list == ['a']
See also findAll and grep when wanting to produce a new list
containing items which match some criteria but leaving the original collection unchanged.
                                        
Parameters:
                                        
condition -  a closure condition
                                    
public boolean removeAll(Object[] items)
                                    
Modifies this collection by removing its elements that are contained
within the specified object array.
See also findAll and grep when wanting to produce a new list
containing items which don't match some criteria while leaving the original collection unchanged.
                                        
Parameters:
                                        
items -  array containing elements to be removed from this collection
                                    
public boolean removeElement(Object o)
                                    
Modifies this collection by removing a single instance of the specified
element from this collection, if it is present. Essentially an alias for
Collection#remove(Object) but with no ambiguity for Collection<Integer>.
Example:
def list = [1, 2, 3, 2]
list.removeElement(2)
assert [1, 3, 2] == list
                                    
public boolean retainAll(Closure condition)
                                    
Modifies this collection so that it retains only its elements
that are matched according to the specified closure condition.  In other words,
removes from this collection all of its elements that don't match.
def list = ['a', 'b']
list.retainAll { it == 'b' }
assert list == ['b']
See also findAll and grep when wanting to produce a new list
containing items which match some criteria but leaving the original collection unchanged.
                                        
Parameters:
                                        
condition -  a closure condition
                                    
public boolean retainAll(Object[] items)
                                    
Modifies this collection so that it retains only its elements that are contained
in the specified array.  In other words, removes from this collection all of
its elements that are not contained in the specified array.
See also grep and findAll when wanting to produce a new list
containing items which match some specified items but leaving the original collection unchanged.
                                        
Parameters:
                                        
items -  array containing elements to be retained from this collection
                                    
public Collection split(Closure closure)
                                    
Splits all items into two collections based on the closure condition.
The first list contains all items which match the closure expression.
The second list all those that don't.
Example usage:
assert [[2,4],[1,3]] == [1,2,3,4].split { it % 2 == 0 }
                                        
Parameters:
                                        
closure -  a closure condition
                                    
public String toListString()
                                    
Returns the string representation of the given list.  The string
displays the contents of the list, similar to a list literal, i.e.
[1, 2, a].
                                    
public String toListString(int maxSize)
                                    
Returns the string representation of the given list.  The string
displays the contents of the list, similar to a list literal, i.e.
[1, 2, a].
                                        
Parameters:
                                        
maxSize -  stop after approximately this many characters and append '...'
                                    
Convert a Collection to a Set. Always returns a new Set
even if the Collection is already a Set.
Example usage:
def result = [1, 2, 2, 2, 3].toSet()
assert result instanceof Set
assert result == [1, 2, 3] as Set
                                    
public Collection unique()
                                    
Modifies this collection to remove all duplicated items, using Groovy's
default number-aware comparator.
assert [1,3] == [1,3,3].unique()
                                    
public Collection unique(boolean mutate)
                                    
Remove all duplicates from a given Collection using Groovy's default number-aware comparator.
If mutate is true, it works by modifying the original object (and also returning it).
If mutate is false, a new collection is returned leaving the original unchanged.
assert [1,3] == [1,3,3].unique()
def orig = [1, 3, 2, 3]
def uniq = orig.unique(false)
assert orig == [1, 3, 2, 3]
assert uniq == [1, 3, 2]
                                    
public Collection unique(boolean mutate, Closure closure)
                                    
A convenience method for making a collection unique using a Closure to determine duplicate (equal) items.
If mutate is true, it works on the receiver object and returns it. If mutate is false, a new collection is returned.
If the closure takes a single parameter, each element from the Collection will be passed to the closure. The closure
should return a value used for comparison (either using Comparable#compareTo(java.lang.Object) or
Object#equals(java.lang.Object)). If the closure takes two parameters, two items from the collection
will be passed as arguments, and the closure should return an int value (with 0 indicating the items are not unique).
def orig = [1, 3, 4, 5]
def uniq = orig.unique(false) { it % 2 }
assert orig == [1, 3, 4, 5]
assert uniq == [1, 4]
def orig = [2, 3, 3, 4]
def uniq = orig.unique(false) { a, b -> a <=> b }
assert orig == [2, 3, 3, 4]
assert uniq == [2, 3, 4]
                                        
Parameters:
                                        
mutate -   false will always cause a new list to be created, true will mutate lists in place
                                        
closure -  a 1 or 2 arg Closure used to determine unique items
                                    
public Collection unique(boolean mutate, Comparator comparator)
                                    
Remove all duplicates from a given Collection.
If mutate is true, it works on the original object (and also returns it). If mutate is false, a new collection is returned.
The order of members in the Collection are compared by the given Comparator.
For each duplicate, the first member which is returned
by the given Collection's iterator is retained, but all other ones are removed.
The given Collection's original order is preserved.
class Person {
    def fname, lname
    String toString() {
        return fname + " " + lname
class PersonComparator implements Comparator {
    int compare(Object o1, Object o2) {
        Person p1 = (Person) o1
        Person p2 = (Person) o2
        if (p1.lname != p2.lname)
            return p1.lname.compareTo(p2.lname)
            return p1.fname.compareTo(p2.fname)
    boolean equals(Object obj) {
        return this.equals(obj)
Person a = new Person(fname:"John", lname:"Taylor")
Person b = new Person(fname:"Clark", lname:"Taylor")
Person c = new Person(fname:"Tom", lname:"Cruz")
Person d = new Person(fname:"Clark", lname:"Taylor")
def list = [a, b, c, d]
List list2 = list.unique(false, new PersonComparator())
assert( list2 != list && list2 == [a, b, c] )
                                        
Parameters:
                                        
mutate -      false will always cause a new collection to be created, true will mutate collections in place
                                        
comparator -  a Comparator
                                    
public Collection unique(Closure closure)
                                    
A convenience method for making a collection unique using a Closure
to determine duplicate (equal) items.
If the closure takes a single parameter, the
argument passed will be each element, and the closure
should return a value used for comparison (either using
Comparable#compareTo(java.lang.Object) or Object#equals(java.lang.Object)).
If the closure takes two parameters, two items from the collection
will be passed as arguments, and the closure should return an
int value (with 0 indicating the items are not unique).
assert [1,4] == [1,3,4,5].unique { it % 2 }
assert [2,3,4] == [2,3,3,4].unique { a, b -> a <=> b }
                                        
Parameters:
                                        
closure -  a 1 or 2 arg Closure used to determine unique items
                                    
public Collection unique(Comparator comparator)
                                    
Remove all duplicates from a given Collection.
Works on the original object (and also returns it).
The order of members in the Collection are compared by the given Comparator.
For each duplicate, the first member which is returned
by the given Collection's iterator is retained, but all other ones are removed.
The given Collection's original order is preserved.
class Person {
    def fname, lname
    String toString() {
        return fname + " " + lname
class PersonComparator implements Comparator {
    int compare(Object o1, Object o2) {
        Person p1 = (Person) o1
        Person p2 = (Person) o2
        if (p1.lname != p2.lname)
            return p1.lname.compareTo(p2.lname)
            return p1.fname.compareTo(p2.fname)
    boolean equals(Object obj) {
        return this.equals(obj)
Person a = new Person(fname:"John", lname:"Taylor")
Person b = new Person(fname:"Clark", lname:"Taylor")
Person c = new Person(fname:"Tom", lname:"Cruz")
Person d = new Person(fname:"Clark", lname:"Taylor")
def list = [a, b, c, d]
List list2 = list.unique(new PersonComparator())
assert( list2 == list && list == [a, b, c] )