[jira] [Created] (SPARK-23911) High-order function: reduce(array, initialState S, inputFunction, outputFunction) → R

["Xiao Li (JIRA)" <ji...@apache.org>]

Xiao Li created SPARK-23911:
-------------------------------

             Summary: High-order function: reduce(array<T>, initialState S, inputFunction<S, T, S>, outputFunction<S, R>) → R
                 Key: SPARK-23911
                 URL: https://issues.apache.org/jira/browse/SPARK-23911
             Project: Spark
          Issue Type: Sub-task
          Components: SQL
    Affects Versions: 2.3.0
            Reporter: Xiao Li


Ref: https://prestodb.io/docs/current/functions/array.html

Returns a single value reduced from array. inputFunction will be invoked for each element in array in order. In addition to taking the element, inputFunction takes the current state, initially initialState, and returns the new state. outputFunction will be invoked to turn the final state into the result value. It may be the identity function (i -> i).
{noformat}
SELECT reduce(ARRAY [], 0, (s, x) -> s + x, s -> s); -- 0
SELECT reduce(ARRAY [5, 20, 50], 0, (s, x) -> s + x, s -> s); -- 75
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> s + x, s -> s); -- NULL
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> s + COALESCE(x, 0), s -> s); -- 75
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> IF(x IS NULL, s, s + x), s -> s); -- 75
SELECT reduce(ARRAY [2147483647, 1], CAST (0 AS BIGINT), (s, x) -> s + x, s -> s); -- 2147483648
SELECT reduce(ARRAY [5, 6, 10, 20], -- calculates arithmetic average: 10.25
              CAST(ROW(0.0, 0) AS ROW(sum DOUBLE, count INTEGER)),
              (s, x) -> CAST(ROW(x + s.sum, s.count + 1) AS ROW(sum DOUBLE, count INTEGER)),
              s -> IF(s.count = 0, NULL, s.sum / s.count));
{noformat}




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