Functions for lists

ListCreate

Construct an empty list. The only argument specifies a string describing the data type of the list cell, or the type itself obtained using relevant functions. YQL doesn't support lists with an unknown cell type.

Type description format documentation.

Examples

SELECT ListCreate(Tuple<String,Double?>);

SELECT ListCreate(OptionalType(DataType("String")));

Signature

ListCreate(T)->List<T>

asList and AsListStrict

Construct a list based on one or more arguments. The argument types must be compatible in the case of AsList and strictly match in the case of AsListStrict.

Examples

SELECT AsList(1, 2, 3, 4, 5);

Signature

AsList(T..)->List<T>

ListLength

The count of items in the list.

Examples

SELECT ListLength(list_column) FROM my_table;

Signature

ListLength(List<T>)->Uint64
ListLength(List<T>?)->Uint64?

ListHasItems

Check that the list contains at least one item.

Examples

SELECT ListHasItems(list_column) FROM my_table;

Signature

ListHasItems(List<T>)->Bool
ListHasItems(List<T>?)->Bool?

ListCollect

Convert a lazy list (which can be built by such functions as ListFilter, ListMap, ListFlatMap) to an eager list. In contrast to a lazy list, where each new pass re-calculates the list contents, in an eager list the content is built at once by consuming more memory.

Examples

SELECT ListCollect(list_column) FROM my_table;

Signature

ListCollect(LazyList<T>)->List<T>
ListCollect(LazyList<T>?)->List<T>?

ListSort, ListSortAsc and ListSortDesc

Sort the list. By default, the ascending sorting order is applied (ListSort is an alias for ListSortAsc).

Arguments:

  1. List.
  2. An optional expression to get the sort key from a list element (it's the element itself by default).

Examples

SELECT ListSortDesc(list_column) FROM my_table;

$list = AsList(
    AsTuple("x", 3),
    AsTuple("xx", 1),
    AsTuple("a", 2)
);

SELECT ListSort($list, ($x) -> {
    RETURN $x.1;
});

Note

The lambda function was used in the example.

Signature

ListSort(List<T>)->List<T>
ListSort(List<T>?)->List<T>?

ListSort(List<T>, (T)->U)->List<T>
ListSort(List<T>?, (T)->U)->List<T>?

ListExtend and ListExtendStrict

Sequentially join lists (concatenation of lists). The arguments can be lists, optional lists, and NULL.
The types of list elements must be compatible in the case of ListExtend and strictly match in the case of ListExtendStrict.
If at least one of the lists is optional, then the result is also optional.
If at least one argument is NULL, then the result type is NULL.

Examples

SELECT ListExtend(
    list_column_1,
    list_column_2,
    list_column_3
) FROM my_table;

$l1 = AsList("a", "b");
$l2 = AsList("b", "c");
$l3 = AsList("d", "e");

SELECT ListExtend($l1, $l2, $l3);  -- ["a","b","b","c","d","e"]

Signature

ListExtend(List<T>..)->List<T>
ListExtend(List<T>?..)->List<T>?

ListUnionAll

Sequentially join lists of structures (concatenation of lists). A field is added to the output list of structures if it exists in at least one source list, but if there is no such field in any list, it is added as NULL. In the case when a field is present in two or more lists, the output field is cast to the common type.

If at least one of the lists is optional, then the result is also optional.

Examples

SELECT ListUnionAll(
    list_column_1,
    list_column_2,
    list_column_3
) FROM my_table;

$l1 = AsList(
    <|value:1|>,
    <|value:2|>
);
$l2 = AsList(
    <|key:"a"|>,
    <|key:"b"|>
);
SELECT ListUnionAll($l1, $l2);  -- result: [("value":1),("value":2),("key":"a"),("key":"b")]
                                -- schema: List<Struct<key : String?, value : Int32?>>

Signature

ListUnionAll(List<Struct<..>>, List<Struct<..>>..)->List<Struct<..>>
ListUnionAll(List<Struct<..>>?, List<Struct<..>>?..)->List<Struct<..>>?

ListZip and ListZipAll

Based on the input lists, build a list of pairs containing the list elements with corresponding indexes (List<Tuple<first_list_element_type,second_list_element_type>>).

The length of the returned list is determined by the shortest list for ListZip and the longest list for ListZipAll.
When the shorter list is exhausted, a NULL value of a relevant optional type.

Examples

SELECT
    ListZip(list_column_1, list_column_2, list_column_3),
    ListZipAll(list_column_1, list_column_2)
FROM my_table;

$l1 = AsList("a", "b");
$l2 = AsList(1, 2, 3);

SELECT ListZip($l1, $l2);  -- [("a",1),("b",2)]
SELECT ListZipAll($l1, $l2);  -- [("a",1),("b",2),(null,3)]

Signature

ListZip(List<T1>, List<T2>)->List<Tuple<T1, T2>>
ListZip(List<T1>?, List<T2>?)->List<Tuple<T1, T2>>?

ListZipAll(List<T1>, List<T2>)->List<Tuple<T1?, T2?>>
ListZipAll(List<T1>?, List<T2>?)->List<Tuple<T1?, T2?>>?

ListEnumerate

Build a list of pairs (Tuple) containing the element number and the element itself (List<Tuple<Uint64,list_element_type>>).

Examples

SELECT ListEnumerate(list_column) FROM my_table;

Signature

ListEnumerate(List<T>)->List<Tuple<Uint64, T>>
ListEnumerate(List<T>?)->List<Tuple<Uint64, T>>?

ListReverse

Reverse the list.

Examples

SELECT ListReverse(list_column) FROM my_table;

Signature

ListReverse(List<T>)->List<T>
ListReverse(List<T>?)->List<T>?

ListSkip

Returns a copy of the list, skipping the specified number of its first elements.

The first argument specifies the source list and the second argument specifies how many elements to skip.

Examples

SELECT
    ListSkip(list_column, 3)
FROM my_table;

$l1 = AsList(1, 2, 3, 4, 5);

SELECT ListSkip($l1, 2);  -- [3,4,5]

Signature

ListSkip(List<T>, Uint64)->List<T>
ListSkip(List<T>?, Uint64)->List<T>?

ListTake

Returns a copy of the list containing a limited number of elements from the second list.

The first argument specifies the source list and the second argument specifies the maximum number of elements to be taken from the beginning of the list.

Examples

SELECT ListTake(list_column, 3) FROM my_table;

$l1 = AsList(1, 2, 3, 4, 5);

SELECT ListTake($l1, 2);  -- [1,2]

Signature

ListTake(List<T>, Uint64)->List<T>
ListTake(List<T>?, Uint64)->List<T>?

ListSample and ListSampleN

Returns a sample of elements from the list without duplicates.

  • ListSample selects each element independently with a specified probability.

  • ListSampleN selects a fixed number of elements (if the list is smaller than the sample size, the original list is returned).

If the probability or sample size is NULL, the original list is returned.

An additional argument is used to control randomness. For more information, see the documentation for Random.

Examples

$list = AsList(1, 2, 3, 4, 5);

SELECT ListSample($list, 0.5);  -- [1, 2, 5]
SELECT ListSampleN($list, 2);  -- [4, 2]

Signature

ListSample(List<T>, Double?[, U])->List<T>
ListSample(List<T>?, Double?[, U])->List<T>?

ListSampleN(List<T>, Uint64?[, U])->List<T>
ListSampleN(List<T>?, Uint64?[, U])->List<T>?

ListShuffle

Returns a copy of the list with the elements rearranged in random order. An additional argument is used to control randomness. For more information, see the documentation for Random.

Examples

$list = AsList(1, 2, 3, 4, 5);

SELECT ListShuffle($list);  -- [1, 3, 5, 2, 4]

Signature

ListShuffle(List<T>[, U])->List<T>
ListShuffle(List<T>?[, U])->List<T>?

ListIndexOf

Searches the list for an element with the specified value and returns its index at the first occurrence. Indexes count from 0. If such element is missing, it returns NULL.

Examples

SELECT
    ListIndexOf(list_column, 123)
FROM my_table;

$l1 = AsList(1, 2, 3, 4, 5);

SELECT ListIndexOf($l1, 2);  -- 1

Signature

ListIndexOf(List<T>, T)->Uint64?
ListIndexOf(List<T>?, T)->Uint64?

ListMap, ListFlatMap and ListFilter

Apply the function specified as the second argument to each list element. The functions differ in their returned result:

  • ListMap returns a list with results.
  • ListFlatMap returns a list with results, combining and expanding the first level of results (lists or optional values) for each item.
  • ListFilter leaves only those elements where the function returned true.

Note

In ListFlatMap, optional values in function results are deprecated, use the combination of ListNotNull and ListMap instead.

Arguments:

  1. Source list.

  2. Functions for processing list elements, such as:

If the source list is optional, then the output list is also optional.

Examples

SELECT
    ListMap(list_column, ($x) -> { RETURN $x > 2; }),
    ListFlatMap(list_column, My::Udf)
FROM my_table;

$list = AsList("a", "b", "c");

$filter = ($x) -> {
    RETURN $x == "b";
};

SELECT ListFilter($list, $filter);  -- ["b"]

$list = AsList(1,2,3,4);
$callable = Python::test(Callable<(Int64)->Bool>, "def test(i): return i % 2");
SELECT ListFilter($list, $callable);  -- [1,3]

Signature

ListMap(List<T>, (T)->U)->List<U>
ListMap(List<T>?, (T)->U)->List<U>?

ListFlatMap(List<T>, (T)->List<U>)->List<U>
ListFlatMap(List<T>?, (T)->List<U>)->List<U>?
ListFlatMap(List<T>, (T)->U?)->List<U>
ListFlatMap(List<T>?, (T)->U?)->List<U>?

ListFilter(List<T>, (T)->Bool)->List<T>
ListFilter(List<T>?, (T)->Bool)->List<T>?

ListNotNull

Applies transformation to the source list, skipping empty optional items and strengthening the item type to non-optional. For a list with non-optional items, it returns the unchanged source list.

If the source list is optional, then the output list is also optional.

Examples

SELECT ListNotNull([1,2]),   -- [1,2]
    ListNotNull([3,null,4]); -- [3,4]

Signature

ListNotNull(List<T?>)->List<T>
ListNotNull(List<T?>?)->List<T>?

ListFlatten

Expands the list of lists into a flat list, preserving the order of items. As the top-level list item, you can use an optional list that is interpreted as an empty list in the case of NULL.

If the source list is optional, then the output list is also optional.

Examples

SELECT ListFlatten([[1,2],[3,4]]),   -- [1,2,3,4]
    ListFlatten([null,[3,4],[5,6]]); -- [3,4,5,6]

Signature

ListFlatten(List<List<T>?>)->List<T>
ListFlatten(List<List<T>?>?)->List<T>?

ListUniq and ListUniqStable

Returns a copy of the list containing only distinct elements. For ListUniq, the order of elements in the resulting list is undefined. For ListUniqStable, elements appear in the same order as in the source list.

Examples

SELECT ListUniq([1, 2, 3, 2, 4, 5, 1]) -- [5, 4, 2, 1, 3]
SELECT ListUniqStable([1, 2, 3, 2, 4, 5, 1]) -- [1, 2, 3, 4, 5]
SELECT ListUniqStable([1, 2, null, 7, 2, 8, null]) -- [1, 2, null, 7, 8]

Signature

ListUniq(List<T>)->List<T>
ListUniq(List<T>?)->List<T>?

ListUniqStable(List<T>)->List<T>
ListUniqStable(List<T>?)->List<T>?

ListAny and ListAll

Returns true for a list of Boolean values if:

  • ListAny: At least one element is true.
  • ListAll: All elements are true.

Otherwise, it returns false.

Behavior with empty lists:

  • ListAny returns false.
  • ListAll returns true.

Examples

SELECT
    ListAll(bool_column),
    ListAny(bool_column)
FROM my_table;

Signature

ListAny(List<Bool>)->Bool
ListAny(List<Bool>?)->Bool?
ListAll(List<Bool>)->Bool
ListAll(List<Bool>?)->Bool?

ListHas

Show whether the list contains the specified element. In this case, NULL values are considered equal to each other. If the input list is NULL, the result is always false.

Examples

SELECT
    ListHas(list_column, "my_needle")
FROM my_table;

$l1 = AsList(1, 2, 3, 4, 5);

SELECT ListHas($l1, 2);  -- true
SELECT ListHas($l1, 6);  -- false

Signature

ListHas(List<T>, U)->Bool
ListHas(List<T>?, U)->Bool

ListHead, ListLast

Returns the first and last item of the list.

Examples

SELECT
    ListHead(numeric_list_column) AS head,
    ListLast(numeric_list_column) AS last
FROM my_table;

Signature

ListHead(List<T>)->T?
ListHead(List<T>?)->T?
ListLast(List<T>)->T?
ListLast(List<T>?)->T?

ListMin, ListMax, ListSum and ListAvg

Apply the appropriate aggregate function to all elements of the numeric list.

Examples

SELECT
    ListMax(numeric_list_column) AS max,
    ListMin(numeric_list_column) AS min,
    ListSum(numeric_list_column) AS sum,
    ListAvg(numeric_list_column) AS avg
FROM my_table;

Signature

ListMin(List<T>)->T?
ListMin(List<T>?)->T?

ListFold, ListFold1

List folding.

Arguments:

  1. List
  2. Initial value U for ListFold, initLambda(item:T)->U for ListFold1
  3. updateLambda(item:T, state:U)->U

Return type:
U for ListFold, optional U for ListFold1.

Examples

$l = [1, 4, 7, 2];
$y = ($x, $y) -> { RETURN $x + $y; };
$z = ($x) -> { RETURN 4 * $x; };

SELECT
    ListFold($l, 6, $y) AS fold,                       -- 20
    ListFold([], 3, $y) AS fold_empty,                 -- 3
    ListFold1($l, $z, $y) AS fold1,                    -- 17
    ListFold1([], $z, $y) AS fold1_empty;              -- Null

Signature

ListFold(List<T>, U, (T, U)->U)->U
ListFold(List<T>?, U, (T, U)->U)->U?

ListFold1(List<T>, (T)->U, (T, U)->U)->U?
ListFold1(List<T>?, (T)->U, (T, U)->U)->U?

ListFoldMap, ListFold1Map

Converts each element i in the list by calling handler(i, state).

Arguments:

  1. List
  2. Initial state S for ListFoldMap, initLambda(item:T)->tuple (U S) for ListFold1Map
  3. handler(item:T, state:S)->tuple (U S)

Return type:
List of elements U.

Examples

$l = [1, 4, 7, 2];
$x = ($i, $s) -> { RETURN ($i * $s, $i + $s); };
$t = ($i) -> { RETURN ($i + 1, $i + 2); };

SELECT
    ListFoldMap([], 1, $x),                -- []
    ListFoldMap($l, 1, $x),                -- [1, 8, 42, 26]
    ListFold1Map([], $t, $x),              -- []
    ListFold1Map($l, $t, $x);              -- [2, 12, 49, 28]

Signature

ListFoldMap(List<T>, S, (T, S)->Tuple<U,S>)->List<U>
ListFoldMap(List<T>?, S, (T, S)->Tuple<U,S>)->List<U>?

ListFold1Map(List<T>, (T)->Tuple<U,S>, (T, S)->Tuple<U,S>)->List<U>
ListFold1Map(List<T>?, (T)->Tuple<U,S>, (T, S)->Tuple<U,S>)->List<U>?

ListFromRange

Generate a sequence of numbers or dates with the specified step. It's similar to xrange in Python 2, but additionally supports dates and floating points.

Arguments:

  1. Start
  2. End
  3. Step. Optional, 1 by default for numeric sequences, 1 day for Date/TzDate, 1 second for Datetime/TzDatetime, and 1 microsecondTimestamp/TzTimestamp/Interval

Features:

  • *The end is not included, i.e. ListFromRange(1,3) == AsList(1,2).
  • The type for the resulting elements is selected as the broadest from the argument types. For example, ListFromRange(1, 2, 0.5) results in a Double list.
  • If start and end have one of the date types, the step must have the Interval type.
  • The list is "lazy", but if it's used incorrectly, it can still consume a lot of RAM.
  • If the step is positive and the end is less than or equal to the start, the result list is empty.
  • If the step is negative and the end is greater than or equal to the start, the result list is empty.
  • If the step is neither positive nor negative (0 or NaN), the result list is empty.
  • If one of the parameters is optional, the result will be an optional list.
  • If one of the parameters is NULL, the result is NULL.

Examples

SELECT
    ListFromRange(-2, 2), -- [-2, -1, 0, 1]
    ListFromRange(2, 1, -0.5); -- [2.0, 1.5]

SELECT ListFromRange(Datetime("2022-05-23T15:30:00Z"), Datetime("2022-05-30T15:30:00Z"), DateTime::IntervalFromDays(1));

Signature

ListFromRange(T{Flags:AutoMap}, T{Flags:AutoMap}, T?)->LazyList<T> -- T is a numeric type
ListFromRange(T{Flags:AutoMap}, T{Flags:AutoMap}, I?)->LazyList<T> -- T is a date/time type; I is an interval

ListReplicate

Creates a list containing multiple copies of the specified value.

Mandatory arguments:

  1. Value.
  2. Number of copies.

Examples

SELECT ListReplicate(true, 3); -- [true, true, true]

Signature

ListReplicate(T, Uint64)->List<T>

ListConcat

Concatenates a list of strings into a single string.
You can set a separator as the second parameter.

Examples

SELECT
    ListConcat(string_list_column),
    ListConcat(string_list_column, "; ")
FROM my_table;

$l1 = AsList("h", "e", "l", "l", "o");

SELECT ListConcat($l1);  -- "hello"
SELECT ListConcat($l1, " ");  -- "h e l l o"

Signature

ListConcat(List<String>)->String?
ListConcat(List<String>?)->String?

ListConcat(List<String>, String)->String?
ListConcat(List<String>?, String)->String?

ListExtract

For a list of structures, it returns a list of contained fields having the specified name.

Examples

SELECT
    ListExtract(struct_list_column, "MyMember")
FROM my_table;

$l = AsList(
    <|key:"a", value:1|>,
    <|key:"b", value:2|>
);
SELECT ListExtract($l, "key");  -- ["a", "b"]

Signature

ListExtract(List<Struct<..>>, String)->List<T>
ListExtract(List<Struct<..>>?, String)->List<T>?

ListTakeWhile, ListSkipWhile

ListTakeWhile returns a list from the beginning while the predicate is true, then the list ends.

ListSkipWhile skips the list segment from the beginning while the predicate is true, then returns the rest of the list disregarding the predicate.
ListTakeWhileInclusive returns a list from the beginning while the predicate is true. Then the list ends, but it also includes the item on which the stopping predicate triggered.
ListSkipWhileInclusive skips a list segment from the beginning while the predicate is true, then returns the rest of the list disregarding the predicate, but excluding the element that matched the predicate and starting with the next element after it.

Mandatory arguments:

  1. List.
  2. Predicate.

If the input list is optional, then the result is also optional.

Examples

$data = AsList(1, 2, 5, 1, 2, 7);

SELECT
    ListTakeWhile($data, ($x) -> {return $x <= 3}), -- [1, 2]
    ListSkipWhile($data, ($x) -> {return $x <= 3}), -- [5, 1, 2, 7]
    ListTakeWhileInclusive($data, ($x) -> {return $x <= 3}), -- [1, 2, 5]
    ListSkipWhileInclusive($data, ($x) -> {return $x <= 3}); -- [1, 2, 7]

Signature

ListTakeWhile(List<T>, (T)->Bool)->List<T>
ListTakeWhile(List<T>?, (T)->Bool)->List<T>?

ListAggregate

Apply the aggregation factory to the passed list.
If the passed list is empty, the aggregation result is the same as for an empty table: 0 for the COUNT function and NULL for other functions.
If the passed list is optional and NULL, the result is also NULL.

Arguments:

  1. List.
  2. Aggregate function factory.

Examples

SELECT ListAggregate(AsList(1, 2, 3), AggregationFactory("Sum")); -- 6

Signature

ListAggregate(List<T>, AggregationFactory)->T
ListAggregate(List<T>?, AggregationFactory)->T?

ToDict and ToMultiDict

Convert a list of tuples containing key-value pairs to a dictionary. If there are conflicting keys in the input list, ToDict leaves the first value and ToMultiDict builds a list of all the values.

It means that:

  • ToDict converts List<Tuple<K, V>> to Dict<K, V>
  • ToMultiDict converts List<Tuple<K, V>> to Dict<K, List<V>>

Optional lists are also supported, resulting in an optional dictionary.

Examples

SELECT
    ToDict(tuple_list_column)
FROM my_table;

$l = AsList(("a",1), ("b", 2), ("a", 3));
SELECT ToDict($l);  -- {"a": 1,"b": 2}

Signature

ToDict(List<Tuple<K,V>>)->Dict<K,V>
ToDict(List<Tuple<K,V>>?)->Dict<K,V>?

ToSet

Converts a list to a dictionary where the keys are unique elements of this list, and values are omitted and have the type Void. For the List<T> list, the result type is Dict<T, Void>.
An optional list is also supported, resulting in an optional dictionary.

Inverse function: get a list of keys for the DictKeys dictionary.

Examples

SELECT
    ToSet(list_column)
FROM my_table;

$l = AsList(1,1,2,2,3);
SELECT ToSet($l);  -- {1,2,3}

Signature

ToSet(List<T>)->Set<T>
ToSet(List<T>?)->Set<T>?

ListFromTuple

Creates a list from a tuple with compatible element types. For an optional tuple, returns an optional list. For a NULL argument, returns NULL. For an empty tuple, returns EmptyList.

Examples

$t = (1,2,3);
SELECT ListFromTuple($t);  -- [1,2,3]

Signature

ListFromTuple(Null)->Null
ListFromTuple(Tuple<>)->EmptyList
ListFromTuple(Tuple<T1,T2,...>)->List<T>
ListFromTuple(Tuple<T1,T2,...>?)->List<T>?

ListToTuple

Creates a tuple from a list and an explicitly specified tuple width. All elements in the resulting tuple will have the same type as the list elements. If the list length doesn't match the specified tuple width, returns an error. For an optional list, returns an optional tuple. For a NULL argument, returns NULL.

Examples

$l = [1,2,3];
SELECT ListToTuple($l, 3);  -- (1,2,3)

Signature

ListToTuple(Null,N)->Null
ListToTuple(EmptyList,N)->()) -- N must be 0
ListToTuple(List<T>, N)->Tuple<T,T,...T> -- tuple width is N
ListToTuple(List<T>?, N)->Tuple<T,T,...T>? -- tuple width is N

ListTop, ListTopAsc, ListTopDesc, ListTopSort, ListTopSortAsc, and ListTopSortDesc

Select the top values from the list. ListTopSort* additionally sorts the list of the returned values. By default, the lowest values are selected. Functions without a suffix are aliases for *Asc functions. *Desc functions select the highest values.

ListTopSort is more efficient than calling ListTop followed by ListSort, because ListTop may partially pre-sort the list when looking for the desired values. However, ListTop is more efficient than ListTopSort if you don't need to sort the output.

Arguments:

  1. List.
  2. Sample size.
  3. An optional expression to get the sort key from a list element (it's the element itself by default).

Signature

ListTop(List<T>{Flags:AutoMap}, N)->List<T>
ListTop(List<T>{Flags:AutoMap}, N, (T)->U)->List<T>

The signatures of other functions match those of ListTop.

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