Array functions

AQL provides functions for higher-level array manipulation. Also see the numeric functions for functions that work on number arrays. If you want to concatenate the elements of an array equivalent to join() in JavaScript, see CONCAT() and CONCAT_SEPARATOR() in the string functions chapter.

Apart from that, AQL also offers several language constructs:

• simple array access of individual elements,
• array operators for array expansion and contraction, optionally with inline filter, limit and projection,
• array comparison operators to compare each element in an array to a value or the elements of another array,
• loop-based operations on arrays using FOR, SORT, LIMIT, as well as COLLECT for grouping, which also offers efficient aggregation.

APPEND()

APPEND(anyArray, values, unique) → newArray

Add all elements of an array to another array. All values are added at the end of the array (right side).

It can also be used to append a single element to an array. It is not necessary to wrap it in an array (unless it is an array itself). You may also use PUSH() instead.

• anyArray (array): array with elements of arbitrary type
• values (array|any): array, whose elements shall be added to anyArray
• unique (bool, optional): if set to true, all duplicate values are removed from the resulting array. If values is an empty array or if either anyArray or values is null, then the other input array is returned unmodified. The default is false.
• returns newArray (array): the modified array

Examples

RETURN APPEND([ 1, 2, 3 ], [ 5, 6, 9 ])

[
  [
    1,
    2,
    3,
    5,
    6,
    9
  ]
]

RETURN APPEND([ 1, 2, 3 ], [ 3, 4, 5, 2, 9 ], true)

[
  [
    1,
    2,
    3,
    4,
    5,
    9
  ]
]

CONTAINS_ARRAY()

This is an alias for POSITION().

COUNT()

This is an alias for LENGTH().

COUNT_DISTINCT()

COUNT_DISTINCT(anyArray) → number

Get the number of distinct elements in an array.

• anyArray (array): array with elements of arbitrary type
• returns number: the number of distinct elements in anyArray.

Examples

RETURN COUNT_DISTINCT([ 1, 2, 3 ])

[
  3
]

RETURN COUNT_DISTINCT([ "yes", "no", "yes", "sauron", "no", "yes" ])

[
  3
]

COUNT_UNIQUE()

This is an alias for COUNT_DISTINCT().

FIRST()

FIRST(anyArray) → firstElement

Get the first element of an array. It is the same as anyArray[0].

• anyArray (array): array with elements of arbitrary type
• returns firstElement (any|null): the first element of anyArray, or null if the array is empty.

Examples

RETURN FIRST([ 1, 2, 3 ])

[
  1
]

RETURN FIRST([])

[
  null
]

FLATTEN()

FLATTEN(anyArray, depth) → flatArray

Turn an array of arrays into a flat array. All array elements in array will be expanded in the result array. Non-array elements are added as they are. The function will recurse into sub-arrays up to the specified depth. Duplicates will not be removed.

Also see array contraction.

• array (array): array with elements of arbitrary type, including nested arrays
• depth (number, optional): flatten up to this many levels, the default is 1
• returns flatArray (array): a flattened array

Examples

RETURN FLATTEN( [ 1, 2, [ 3, 4 ], 5, [ 6, 7 ], [ 8, [ 9, 10 ] ] ] )

[
  [
    1,
    2,
    3,
    4,
    5,
    6,
    7,
    8,
    [
      9,
      10
    ]
  ]
]

To fully flatten the example array, use a depth of 2:

RETURN FLATTEN( [ 1, 2, [ 3, 4 ], 5, [ 6, 7 ], [ 8, [ 9, 10 ] ] ], 2 )

[
  [
    1,
    2,
    3,
    4,
    5,
    6,
    7,
    8,
    9,
    10
  ]
]

INTERLEAVE()

Introduced in: v3.7.1

INTERLEAVE(array1, array2, ... arrayN) → newArray

Accepts an arbitrary number of arrays and produces a new array with the elements interleaved. It iterates over the input arrays in a round robin fashion, picks one element from each array per iteration, and combines them in that sequence into a result array. The input arrays can have different amounts of elements.

• arrays (array, repeatable): an arbitrary number of arrays as multiple arguments (at least 2)
• returns newArray (array): the interleaved array

Examples

RETURN INTERLEAVE( [1, 1, 1], [2, 2, 2], [3, 3, 3] )

[
  [
    1,
    2,
    3,
    1,
    2,
    3,
    1,
    2,
    3
  ]
]

RETURN INTERLEAVE( [ 1 ], [2, 2], [3, 3, 3] )

[
  [
    1,
    2,
    3,
    2,
    3,
    3
  ]
]

FOR v, e, p IN 1..3 OUTBOUND 'places/Toronto' GRAPH 'kShortestPathsGraph'
RETURN INTERLEAVE(p.vertices[*]._id, p.edges[*]._id)

[
  [
    "places/Toronto",
    "connections/71058",
    "places/Winnipeg"
  ],
  [
    "places/Toronto",
    "connections/71058",
    "places/Winnipeg",
    "connections/71060",
    "places/Toronto"
  ],
  [
    "places/Toronto",
    "connections/71058",
    "places/Winnipeg",
    "connections/71062",
    "places/Saskatoon"
  ],
  [
    "places/Toronto",
    "connections/71058",
    "places/Winnipeg",
    "connections/71062",
    "places/Saskatoon",
    "connections/71064",
    "places/Winnipeg"
  ],
  [
    "places/Toronto",
    "connections/71058",
    "places/Winnipeg",
    "connections/71062",
    "places/Saskatoon",
    "connections/71066",
    "places/Edmonton"
  ]
]

INTERSECTION()

INTERSECTION(array1, array2, ... arrayN) → newArray

Return the intersection of all arrays specified. The result is an array of values that occur in all arguments.

Other set operations are UNION(), MINUS() and OUTERSECTION().

• arrays (array, repeatable): an arbitrary number of arrays as multiple arguments (at least 2)
• returns newArray (array): a single array with only the elements, which exist in all provided arrays. The element order is random. Duplicates are removed.

Examples

RETURN INTERSECTION( [1,2,3,4,5], [2,3,4,5,6], [3,4,5,6,7] )

[
  [
    5,
    4,
    3
  ]
]

RETURN INTERSECTION( [2,4,6], [8,10,12], [14,16,18] )

[
  []
]

JACCARD()

Introduced in: v3.7.0

JACCARD(array1, array2) → jaccardIndex

Calculate the Jaccard index of two arrays.

This similarity measure is also known as Intersection over Union and could be computed (less efficient and more verbose) as follows:

COUNT(a) == 0 && COUNT(b) == 0
? 1 // two empty sets have a similarity of 1 by definition
: COUNT(INTERSECTION(array1, array2)) / COUNT(UNION_DISTINCT(array1, array2))

• array1 (array): array with elements of arbitrary type
• array2 (array): array with elements of arbitrary type
• returns jaccardIndex (number): calculated Jaccard index of the input arrays array1 and array2

RETURN JACCARD( [1,2,3,4], [3,4,5,6] )

[
  0.3333333333333333
]

RETURN JACCARD( [1,1,2,2,2,3], [2,2,3,4] )

[
  0.5
]

RETURN JACCARD( [1,2,3], [] )

[
  0
]

RETURN JACCARD( [], [] )

[
  1
]

LAST()

LAST(anyArray) → lastElement

Get the last element of an array. It is the same as anyArray[-1].

• anyArray (array): array with elements of arbitrary type
• returns lastElement (any|null): the last element of anyArray or null if the array is empty.

Example

RETURN LAST( [1,2,3,4,5] )

[
  5
]

LENGTH()

LENGTH(anyArray) → length

Determine the number of elements in an array.

• anyArray (array): array with elements of arbitrary type
• returns length (number): the number of array elements in anyArray.

LENGTH() can also determine the number of attribute keys of an object / document, the amount of documents in a collection and the character length of a string.

Examples

RETURN LENGTH( "🥑" )

[
  1
]

RETURN LENGTH( 1234 )

[
  4
]

RETURN LENGTH( [1,2,3,4,5,6,7] )

[
  7
]

RETURN LENGTH( false )

[
  0
]

RETURN LENGTH( {a:1, b:2, c:3, d:4, e:{f:5,g:6}} )

[
  5
]

MINUS()

MINUS(array1, array2, ... arrayN) → newArray

Return the difference of all arrays specified.

Other set operations are UNION(), INTERSECTION() and OUTERSECTION().

• arrays (array, repeatable): an arbitrary number of arrays as multiple arguments (at least 2)
• returns newArray (array): an array of values that occur in the first array, but not in any of the subsequent arrays. The order of the result array is undefined and should not be relied on. Duplicates will be removed.

Example

RETURN MINUS( [1,2,3,4], [3,4,5,6], [5,6,7,8] )

[
  [
    2,
    1
  ]
]

NTH()

NTH(anyArray, position) → nthElement

Get the element of an array at a given position. It is the same as anyArray[position] for positive positions, but does not support negative positions.

• anyArray (array): array with elements of arbitrary type
• position (number): position of desired element in array, positions start at 0
• returns nthElement (any|null): the array element at the given position. If position is negative or beyond the upper bound of the array, then null will be returned.

Examples

RETURN NTH( [ "foo", "bar", "baz" ], 2 )

[
  "baz"
]

RETURN NTH( [ "foo", "bar", "baz" ], 3 )

[
  null
]

RETURN NTH( [ "foo", "bar", "baz" ], -1 )

[
  null
]

OUTERSECTION()

OUTERSECTION(array1, array2, ... arrayN) → newArray

Return the values that occur only once across all arrays specified.

Other set operations are UNION(), MINUS() and INTERSECTION().

• arrays (array, repeatable): an arbitrary number of arrays as multiple arguments (at least 2)
• returns newArray (array): a single array with only the elements that exist only once across all provided arrays. The element order is random.

Example

RETURN OUTERSECTION( [ 1, 2, 3 ], [ 2, 3, 4 ], [ 3, 4, 5 ] )

[
  [
    5,
    1
  ]
]

POP()

POP(anyArray) → newArray

Remove the last element of array.

To append an element (right side), see PUSH().
To remove the first element, see SHIFT().
To remove an element at an arbitrary position, see REMOVE_NTH().

• anyArray (array): an array with elements of arbitrary type
• returns newArray (array): anyArray without the last element. If it’s already empty or has only a single element left, an empty array is returned.

Examples

RETURN POP( [ 1, 2, 3, 4 ] )

[
  [
    1,
    2,
    3
  ]
]

RETURN POP( [ 1 ] )

[
  []
]

POSITION()

POSITION(anyArray, search, returnIndex) → position

Return whether search is contained in array. Optionally return the position.

• anyArray (array): the haystack, an array with elements of arbitrary type
• search (any): the needle, an element of arbitrary type
• returnIndex (bool, optional): if set to true, the position of the match is returned instead of a boolean. The default is false.
• returns position (bool|number): true if search is contained in anyArray, false otherwise. If returnIndex is enabled, the position of the match is returned (positions start at 0), or -1 if it’s not found.

If you want to check if a value is in an array, you can alternatively use the IN operator, for example, 3 IN [1, 2, 3] instead of POSITION([1, 2, 3], 3).

To determine if or at which position a string occurs in another string, see the CONTAINS() string function.

Examples

Test whether a value is contained in an array:

RETURN POSITION( [2,4,6,8], 4 )

[
  true
]

Return the position of the match, i.e. the array index, or -1 if the value is not contained in the array:

RETURN POSITION( [2,4,6,8], 4, true )

[
  1
]

If you want to search a list of objects, you can use the array expansion operator [*]. For example, you can get an attribute from each object using the operator, and then determine the array index of the first match using the POSITION() function:

LET arr = [ { value: "foo" }, { value: "bar" }, { value: "baz" }, { value: "bay"} ]
RETURN POSITION(arr[*].value, "baz", true)

[
  2
]

If you are not interested in the actual position but only want to check for existence, you may use the IN operator instead of calling POSITION(), like "baz" IN arr[*].value.

PUSH()

PUSH(anyArray, value, unique) → newArray

Append value to anyArray (right side).

To remove the last element, see POP().
To prepend a value (left side), see UNSHIFT().
To append multiple elements, see APPEND().

• anyArray (array): array with elements of arbitrary type
• value (any): an element of arbitrary type
• unique (bool): if set to true, then value is not added if already present in the array. The default is false.
• returns newArray (array): anyArray with value added at the end (right side)

Note: The unique flag only controls if value is added if it’s already present in anyArray. Duplicate elements that already exist in anyArray will not be removed. To make an array unique, use the UNIQUE() function.

Examples

RETURN PUSH([ 1, 2, 3 ], 4)

[
  [
    1,
    2,
    3,
    4
  ]
]

RETURN PUSH([ 1, 2, 2, 3 ], 2, true)

[
  [
    1,
    2,
    2,
    3
  ]
]

REMOVE_NTH()

REMOVE_NTH(anyArray, position) → newArray

Remove the element at position from the anyArray.

To remove the first element, see SHIFT().
To remove the last element, see POP().

• anyArray (array): array with elements of arbitrary type
• position (number): the position of the element to remove. Positions start at 0. Negative positions are supported, with -1 being the last array element. If position is out of bounds, the array is returned unmodified.
• returns newArray (array): anyArray without the element at position

Examples

RETURN REMOVE_NTH( [ "a", "b", "c", "d", "e" ], 1 )

[
  [
    "a",
    "c",
    "d",
    "e"
  ]
]

RETURN REMOVE_NTH( [ "a", "b", "c", "d", "e" ], -2 )

[
  [
    "a",
    "b",
    "c",
    "e"
  ]
]

REPLACE_NTH()

Introduced in: v3.7.0

REPLACE_NTH(anyArray, position, replaceValue, defaultPaddingValue) → newArray

Replace the element at position in anyArray with replaceValue.

• anyArray (array): array with elements of arbitrary type
• position (number): the position of the element to replace. Positions start at 0. Negative positions are supported, with -1 being the last array element. If a negative position is out of bounds, then it is set to the first element (0)
• replaceValue the value to be inserted at position
• defaultPaddingValue to be used for padding if position is two or more elements beyond the last element in anyArray
• returns newArray (array): anyArray with the element at position replaced by replaceValue, or appended to anyArray and possibly padded by defaultPaddingValue

It is allowed to specify a position beyond the upper array boundary:

• replaceValue is appended if position is equal to the array length
• if it is higher, defaultPaddingValue is appended to anyArray as many times as needed to place replaceValue at position
• if no defaultPaddingValue is supplied in above case, then a query error is raised

Examples

RETURN REPLACE_NTH( [ "a", "b", "c" ], 1 , "z")

[
  [
    "a",
    "z",
    "c"
  ]
]

RETURN REPLACE_NTH( [ "a", "b", "c" ], 3 , "z")

[
  [
    "a",
    "b",
    "c",
    "z"
  ]
]

RETURN REPLACE_NTH( [ "a", "b", "c" ], 6, "z", "y" )

[
  [
    "a",
    "b",
    "c",
    "y",
    "y",
    "y",
    "z"
  ]
]

RETURN REPLACE_NTH( [ "a", "b", "c" ], -1, "z" )

[
  [
    "a",
    "b",
    "z"
  ]
]

RETURN REPLACE_NTH( [ "a", "b", "c" ], -9, "z" )

[
  [
    "z",
    "b",
    "c"
  ]
]

Trying to access out of bounds, without providing a padding value will result in an error:

arangosh> db._query('RETURN REPLACE_NTH( [ "a", "b", "c" ], 6 , "z")');

[ArangoError 1542: AQL: invalid argument type in call to function 'REPLACE_NTH()' (while optimizing ast)]

REMOVE_VALUE()

REMOVE_VALUE(anyArray, value, limit) → newArray

Remove all occurrences of value in anyArray. Optionally with a limit to the number of removals.

• anyArray (array): array with elements of arbitrary type
• value (any): an element of arbitrary type
• limit (number, optional): cap the number of removals to this value
• returns newArray (array): anyArray with value removed

Examples

RETURN REMOVE_VALUE( [ "a", "b", "b", "a", "c" ], "a" )

[
  [
    "b",
    "b",
    "c"
  ]
]

RETURN REMOVE_VALUE( [ "a", "b", "b", "a", "c" ], "a", 1 )

[
  [
    "b",
    "b",
    "a",
    "c"
  ]
]

REMOVE_VALUES()

REMOVE_VALUES(anyArray, values) → newArray

Remove all occurrences of any of the values from anyArray.

• anyArray (array): array with elements of arbitrary type
• values (array): an array with elements of arbitrary type, that shall be removed from anyArray
• returns newArray (array): anyArray with all individual values removed

Example

RETURN REMOVE_VALUES( [ "a", "a", "b", "c", "d", "e", "f" ], [ "a", "f", "d" ] )

[
  [
    "b",
    "c",
    "e"
  ]
]

REVERSE()

REVERSE(anyArray) → reversedArray

Return an array with its elements reversed.

• anyArray (array): array with elements of arbitrary type
• returns reversedArray (array): a new array with all elements of anyArray in reversed order

Example

RETURN REVERSE ( [2,4,6,8,10] )

[
  [
    10,
    8,
    6,
    4,
    2
  ]
]

SHIFT()

SHIFT(anyArray) → newArray

Remove the first element of anyArray.

To prepend an element (left side), see UNSHIFT().
To remove the last element, see POP().
To remove an element at an arbitrary position, see REMOVE_NTH().

• anyArray (array): array with elements with arbitrary type
• returns newArray (array): anyArray without the left-most element. If anyArray is already empty or has only one element left, an empty array is returned.

Examples

RETURN SHIFT( [ 1, 2, 3, 4 ] )

[
  [
    2,
    3,
    4
  ]
]

RETURN SHIFT( [ 1 ] )

[
  []
]

SLICE()

SLICE(anyArray, start, length) → newArray

Extract a slice of anyArray.

• anyArray (array): array with elements of arbitrary type
• start (number): start extraction at this element. Positions start at 0. Negative values indicate positions from the end of the array.
• length (number, optional): extract up to length elements, or all elements from start up to length if negative (exclusive)
• returns newArray (array): the specified slice of anyArray. If length is not specified, all array elements starting at start will be returned.

Examples

RETURN SLICE( [ 1, 2, 3, 4, 5 ], 0, 1 )

[
  [
    1
  ]
]

RETURN SLICE( [ 1, 2, 3, 4, 5 ], 1, 2 )

[
  [
    2,
    3
  ]
]

RETURN SLICE( [ 1, 2, 3, 4, 5 ], 3 )

[
  [
    4,
    5
  ]
]

RETURN SLICE( [ 1, 2, 3, 4, 5 ], 1, -1 )

[
  [
    2,
    3,
    4
  ]
]

RETURN SLICE( [ 1, 2, 3, 4, 5 ], 0, -2 )

[
  [
    1,
    2,
    3
  ]
]

RETURN SLICE( [ 1, 2, 3, 4, 5 ], -3, 2 )

[
  [
    3,
    4
  ]
]

SORTED()

SORTED(anyArray) → newArray

Sort all elements in anyArray. The function will use the default comparison order for AQL value types.

• anyArray (array): array with elements of arbitrary type
• returns newArray (array): anyArray, with elements sorted

Example

RETURN SORTED( [ 8,4,2,10,6 ] )

[
  [
    2,
    4,
    6,
    8,
    10
  ]
]

SORTED_UNIQUE()

SORTED_UNIQUE(anyArray) → newArray

Sort all elements in anyArray. The function will use the default comparison order for AQL value types. Additionally, the values in the result array will be made unique.

• anyArray (array): array with elements of arbitrary type
• returns newArray (array): anyArray, with elements sorted and duplicates removed

Example

RETURN SORTED_UNIQUE( [ 8,4,2,10,6,2,8,6,4 ] )

[
  [
    2,
    4,
    6,
    8,
    10
  ]
]

UNION()

UNION(array1, array2, ... arrayN) → newArray

Return the union of all arrays specified.

Other set operations are MINUS(), INTERSECTION() and OUTERSECTION().

• arrays (array, repeatable): an arbitrary number of arrays as multiple arguments (at least 2)
• returns newArray (array): all array elements combined in a single array, in any order

Examples

RETURN UNION(
  [ 1, 2, 3 ],
  [ 1, 2 ]
)

[
  [
    1,
    2,
    3,
    1,
    2
  ]
]

Note: No duplicates will be removed. In order to remove duplicates, please use either UNION_DISTINCT() or apply UNIQUE() on the result of UNION():

RETURN UNIQUE(
  UNION(
      [ 1, 2, 3 ],
      [ 1, 2 ]
  )
)

[
  [
    1,
    2,
    3
  ]
]

UNION_DISTINCT()

UNION_DISTINCT(array1, array2, ... arrayN) → newArray

Return the union of distinct values of all arrays specified.

• arrays (array, repeatable): an arbitrary number of arrays as multiple arguments (at least 2)
• returns newArray (array): the elements of all given arrays in a single array, without duplicates, in any order

Example

RETURN UNION_DISTINCT(
  [ 1, 2, 3 ],
  [ 1, 2 ]
)

[
  [
    1,
    3,
    2
  ]
]

UNIQUE()

UNIQUE(anyArray) → newArray

Return all unique elements in anyArray. To determine uniqueness, the function will use the comparison order.

• anyArray (array): array with elements of arbitrary type
• returns newArray (array): anyArray without duplicates, in any order

Example

RETURN UNIQUE( [ 1,2,2,3,3,3,4,4,4,4,5,5,5,5,5 ] )

[
  [
    1,
    2,
    3,
    4,
    5
  ]
]

UNSHIFT()

UNSHIFT(anyArray, value, unique) → newArray

Prepend value to anyArray (left side).

To remove the first element, see SHIFT().
To append a value (right side), see PUSH().

• anyArray (array): array with elements of arbitrary type
• value (any): an element of arbitrary type
• unique (bool): if set to true, then value is not added if already present in the array. The default is false.
• returns newArray (array): anyArray with value added at the start (left side)

Note: The unique flag only controls if value is added if it’s already present in anyArray. Duplicate elements that already exist in anyArray will not be removed. To make an array unique, use the UNIQUE() function.

Examples

RETURN UNSHIFT( [ 1, 2, 3 ], 4 )

[
  [
    4,
    1,
    2,
    3
  ]
]

RETURN UNSHIFT( [ 1, 2, 3 ], 2, true )

[
  [
    1,
    2,
    3
  ]
]