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https://issues.apache.org/jira/browse/SPARK-23911?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16567791#comment-16567791
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Takuya Ueshin commented on SPARK-23911:
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[~smilegator] [~hvanhovell] I'd use {{aggregate}} instead of {{reduce}} for
this function name because {{aggregate}} better fits the functionality of the
function. WDYT?
> 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
> Assignee: Herman van Hovell
> Priority: Major
>
> 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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