java.util
Class Collection

assert [String, Long, Integer] == ["a",5L,2]["class"]

asBoolean

public boolean asBoolean()

 

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

Returns:

the boolean value

Since:

1.7.0

asImmutable

public Collection asImmutable()

 

A convenience method for creating an immutable Collection.

def mutable = [1,2,3]
def immutable = mutable.asImmutable()
mutable << 4
try {
  immutable << 4
  assert false
} catch (UnsupportedOperationException) {
  assert true
}

Returns:

an immutable Collection

Since:

1.5.0

See:

Collections#unmodifiableCollection.

asList

public List asList()

 

Converts this collection to a List.

assert new HashSet().asList() instanceof List

Returns:

a newly created List if this collection is not already a List

Since:

1.0

asSynchronized

public Collection asSynchronized()

 

A convenience method for creating a synchronized Collection.

Returns:

a synchronized Collection

Since:

1.0

See:

Collections#synchronizedCollection.

asType

public Object asType(Class)

 

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 {link #asType(Object,Class)}. If this collection is already of the given type, the same instance is returned.

Parameters:

clazz - the desired class.

Returns:

the object resulting from this type conversion

Since:

1.0

See:

Object#asType.

collect

public List collect(Closure)

 

Iterates through this collection transforming each entry into a new value using the closure as a transformer, returning a list of transformed values.

assert [2,4,6] == [1,2,3].collect { it * 2 }

Parameters:

closure - the closure used for mapping.

Returns:

a List of the transformed values

Since:

1.0

collect

public Collection collect(Collection, Closure)

 

Iterates through this collection transforming each value into a new value using the closure as a transformer, returning an initial collection plus the transformed values.

assert [1,2,3] as HashSet == [2,4,5,6].collect(new HashSet()) { (int)(it / 2) }

Parameters:

collection - an initial Collection to which the transformed values are added.

closure - the closure used to transform each element of the collection.

Returns:

the resulting collection of transformed values

Since:

1.0

collectAll

public List collectAll(Closure)

 

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],[]].collectAll { it * 2 }

Parameters:

closure - the closure used to transform each element of the collection.

Returns:

the resultant collection

Since:

1.5.2

collectAll

public Collection collectAll(Collection, Closure)

 

Recursively iterates through this collection transforming each non-Collection value into a new value using the closure as a transformer. Returns a potentially nested collection of transformed values.

def x = [1,[2,3],[4],[]].collectAll(new Vector()) { it * 2 }
assert x == [2,[4,6],[8],[]]
assert x instanceof Vector

Parameters:

collection - an initial Collection to which the transformed values are added.

closure - the closure used to transform each element of the collection.

Returns:

the resultant collection

Since:

1.5.2

combinations

public List combinations()

 

Adds GroovyCollections#combinations(Collection) as a method on collections.

assert [['a', 'b'],[1, 2, 3]].combinations() == [['a', 1], ['b', 1], ['a', 2], ['b', 2], ['a', 3], ['b', 3]]

Returns:

a List of the combinations found

Since:

1.5.0

See:

GroovyCollections#combinations.

count

public Number count(Object)

 

Counts the number of occurrences of the given value inside this collection. Comparison is done using Groovy's == operator (using compareTo(value) == 0 or equals(value) ).

assert [2,4,2,1,3,5,2,4,3].count(4) == 2

Parameters:

value - the value being searched for.

Returns:

the number of occurrences

Since:

1.0

disjoint

public boolean disjoint(Collection)

 

Returns true if the intersection of two collections is empty.

assert [1,2,3].disjoint([3,4,5]) == false

assert [1,2].disjoint([3,4]) == true

Parameters:

right - a Collection.

Returns:

boolean true if the intersection of two collections is empty, false otherwise.

Since:

1.0

eachPermutation

public Iterator eachPermutation(Closure)

 

Iterates over all permutations of a collection, running a closure for each iteration.

def permutations = []
[1, 2, 3].eachPermutation{ permutations << it }
assert permutations == [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

Parameters:

closure - the closure to call for each permutation.

Returns:

the permutations from the list

Since:

1.7.0

find

public Object find(Closure)

 

Finds the first value matching the closure condition. Example:

def list = [1,2,3]
assert 2 == list.find { it > 1 }

Parameters:

closure - a closure condition.

Returns:

the first Object found

Since:

1.0

findAll

public Collection findAll(Closure)

 

Finds all values matching the closure condition.

assert [2,4] == [1,2,3,4].findAll { it % 2 == 0 }

Parameters:

closure - a closure condition.

Returns:

a Collection of matching values

Since:

1.5.6

flatten

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()

Returns:

a flattened Collection

Since:

1.6.0

flatten

public Collection flatten(Closure)

 

Flatten a collection. This collection and any nested arrays or collections have their contents (recursively) added to the new collection. For any non-Array, non-Collection object which represents some sort of collective type, the supplied closure should yield the contained items; otherwise, the closure should just return any element which corresponds to a leaf.

Parameters:

flattenUsing - a closure to determine how to flatten non-Array, non-Collection elements.

Returns:

a flattened Collection

Since:

1.6.0

getAt

public List getAt(String)

 

Support the subscript operator for List

assert [String, Long, Integer] == ["a",5L,2]["class"]

Parameters:

property - a String.

Returns:

a List

Since:

1.0

groupBy

public Map groupBy(Closure)

 

Sorts all collection members into groups determined by the supplied mapping closure. The closure should return the key that this item should be grouped by. The returned LinkedHashMap will have an entry for each distinct key returned from the closure, with each value being a list of items for that group.

assert [0:[2,4,6], 1:[1,3,5]] == [1,2,3,4,5,6].groupBy { it % 2 }

Parameters:

closure - a closure mapping entries on keys.

Returns:

a new Map grouped by keys

Since:

1.0

inject

public Object inject(Object, Closure)

 

Iterates through the given collection, passing in the initial value to the closure along with the current iterated item then passing into the next iteration the value of the previous closure.

assert 1*1*2*3*4 == [1,2,3,4].inject(1) { acc, val -> acc * val }

Parameters:

value - a value.

closure - a closure.

Returns:

the last value of the last iteration

Since:

1.0

intersect

public Collection intersect(Collection)

 

Create a Collection composed of the intersection of both collections. Any elements that exist in both collections are added to the resultant collection.

assert [4,5] == [1,2,3,4,5].intersect([4,5,6,7,8])

Parameters:

right - a Collection.

Returns:

a Collection as an intersection of both collections

Since:

1.5.6

isCase

public boolean isCase(Object)

 

'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.

Returns:

true if the caseValue is deemed to contain the switchValue

Since:

1.0

See:

Collection#contains.

join

public String join(String)

 

Concatenates the toString() representation of each item in this collection, with the given String as a separator between each item.

assert "1, 2, 3" == [1,2,3].join(", ")

Parameters:

separator - a String separator.

Returns:

the joined String

Since:

1.0

leftShift

public Collection leftShift(Object)

 

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..

Returns:

same collection, after the value was added to it.

Since:

1.0

max

public Object max()

 

Adds max() method to Collection objects.

assert 5 == [2,3,1,5,4].max()

Returns:

the maximum value

Since:

1.0

See:

GroovyCollections#max.

max

public Object max(Closure)

 

Selects the maximum value found in the collection using the closure to determine the correct ordering.

If the closure has two parameters it is used like a traditional Comparator. I.e. it should compare its two parameters for order, returning a negative integer, zero, or a positive integer when the first parameter is less than, equal to, or greater than the second respectively. Otherwise, the Closure is assumed to take a single parameter and return a Comparable (typically an Integer) which is then used for further comparison.

assert "hello" == ["hello","hi","hey"].max { it.length() }

assert "hello" == ["hello","hi","hey"].max { a, b -> a.length() <=> b.length() }

Parameters:

closure - a 1 or 2 arg Closure used to determine the correct ordering.

Returns:

the maximum value

Since:

1.0

max

public Object max(Comparator)

 

Selects the maximum value found in the collection using the given comparator.

assert "hello" == ["hello","hi","hey"].max( { a, b -> a.length() <=> b.length() } as Comparator )

Parameters:

comparator - a Comparator.

Returns:

the maximum value

Since:

1.0

min

public Object min()

 

Adds min() method to Collection objects.

assert 2 == [4,2,5].min()

Returns:

the minimum value

Since:

1.0

See:

GroovyCollections#min.

min

public Object min(Comparator)

 

Selects the minimum value found in the collection using the given comparator.

assert "hi" == ["hello","hi","hey"].min( { a, b -> a.length() <=> b.length() } as Comparator )

Parameters:

comparator - a Comparator.

Returns:

the minimum value

Since:

1.0

min

public Object min(Closure)

 

Selects the minimum value found in the collection using the closure to determine the correct ordering.

If the closure has two parameters it is used like a traditional Comparator. I.e. it should compare its two parameters for order, returning a negative integer, zero, or a positive integer when the first parameter is less than, equal to, or greater than the second respectively. Otherwise, the Closure is assumed to take a single parameter and return a Comparable (typically an Integer) which is then used for further comparison.

assert "hi" == ["hello","hi","hey"].min { it.length() } 

Parameters:

closure - a 1 or 2 arg Closure used to determine the correct ordering.

Returns:

the minimum value

Since:

1.0

multiply

public List multiply(Number)

 

Create a List composed of the elements of this list, repeated a certain number of times. Note that for non-primitive elements, multiple references to the same instance will be added.

assert [1,2,3,1,2,3] == [1,2,3] * 2

Parameters:

factor - the number of times to append.

Returns:

the multiplied list

Since:

1.0

plus

public Collection plus(Collection)

 

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.

Returns:

the merged Collection

Since:

1.5.0

plus

public Collection plus(Object)

 

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.

Returns:

the resulting Collection

Since:

1.5.0

sort

public List sort()

 

Sorts the given collection into a sorted list. The collection items are assumed to be comparable.

assert [1,2,3] == [3,1,2].sort()

Returns:

the sorted collection as a List

Since:

1.0

sort

public List sort(Comparator)

 

Sorts the Collection using the given comparator. The elements are sorted into a new list, and the existing collection is unchanged.

assert ["hi","hey","hello"] == ["hello","hi","hey"].sort( { a, b -> a.length() <=> b.length() } as Comparator )

Parameters:

comparator - a Comparator used for the comparison.

Returns:

a newly created sorted List

Since:

1.0

sort

public List sort(Closure)

 

Sorts this Collection using the closure to determine the correct ordering.

If the closure has two parameters it is used like a traditional Comparator. I.e. it should compare its two parameters for order, returning a negative integer, zero, or a positive integer when the first parameter is less than, equal to, or greater than the second respectively. Otherwise, the Closure is assumed to take a single parameter and return a Comparable (typically an Integer) which is then used for further comparison.

assert ["hi","hey","hello"] == ["hello","hi","hey"].sort { it.length() }

assert ["hi","hey","hello"] == ["hello","hi","hey"].sort { a, b -> a.length() <=> b.length() }

Parameters:

closure - a 1 or 2 arg Closure used to determine the correct ordering.

Returns:

a newly created sorted List

Since:

1.0

split

public Collection split(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.

assert [[2,4],[1,3]] == [1,2,3,4].split { it % 2 == 0 }

Parameters:

closure - a closure condition.

Returns:

a List containing whose first item is the accepted values and whose second item is the rejected values

Since:

1.6.0

sum

public Object sum()

 

Sums the items in a collection. This is equivalent to invoking the "plus" method on all items in the collection.

assert 1+2+3+4 == [1,2,3,4].sum()

Returns:

The sum of all of the items

Since:

1.0

sum

public Object sum(Object)

 

Sums the items in a collection, adding the result to some initial value.

assert 5+1+2+3+4 == [1,2,3,4].sum(5)

Parameters:

initialValue - the items in the collection will be summed to this initial value.

Returns:

The sum of all of the items.

Since:

1.5.0

sum

public Object sum(Closure)

 

Sums the result of apply a closure to each item of a collection. coll.sum(closure) is equivalent to: coll.collect(closure).sum().

assert 4+6+10+12 == [2,3,5,6].sum() { it * 2 }

Parameters:

closure - a single parameter closure that returns a numeric value..

Returns:

The sum of the values returned by applying the closure to each item of the collection.

Since:

1.0

sum

public Object sum(Object, Closure)

 

Sums the result of applying a closure to each item of a collection to some initial value. coll.sum(initVal, closure) is equivalent to: coll.collect(closure).sum(initVal).

assert 50+4+6+10+12 == [2,3,5,6].sum(50) { it * 2 }

Parameters:

closure - a single parameter closure that returns a numeric value..

initialValue - the closure results will be summed to this initial value.

Returns:

The sum of the values returned by applying the closure to each item of the collection.

Since:

1.5.0

toList

public List toList()

 

Convert a collection to a List.

def x = [1,2,3] as HashSet
assert x.class == HashSet
assert x.toList() instanceof List

Returns:

a List

Since:

1.0

toListString

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].

Returns:

the string representation

Since:

1.0

unique

public Collection unique()

 

Modifies this collection to remove all duplicated items, using the default comparator.

assert [1,3] == [1,3,3].unique()

Returns:

the now modified collection

Since:

1.0

unique

public Collection unique(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 or Object#equals). 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.

Returns:

self without any duplicates

Since:

1.0

unique

public Collection unique(Comparator)

 

Remove all duplicates from a given Collection. Works on the receiver object and 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
        public String toString() {
            return fname + " " + lname
        }
    }

    class PersonComparator implements Comparator {
        public 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)
            else
                return p1.fname.compareTo(p2.fname)
        }

        public 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] )

Parameters:

comparator - a Comparator.

Returns:

self the now modified collection without duplicates

Since:

1.0