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Standard Aggregate Functions

[[functions]] .Standard Aggregate Functions [align="center",cols="1m,2",width="100%",options="header"] |=== | Name | Description

| approx_count_distinct a| [[approx_count_distinct]]

[source, scala]

approx_count_distinct(e: Column): Column approx_count_distinct(columnName: String): Column approx_count_distinct(e: Column, rsd: Double): Column approx_count_distinct(columnName: String, rsd: Double): Column

| avg a| [[avg]]

[source, scala]

avg(e: Column): Column avg(columnName: String): Column

| collect_list a| [[collect_list]]

[source, scala]

collect_list(e: Column): Column collect_list(columnName: String): Column

| collect_set a| [[collect_set]]

[source, scala]

collect_set(e: Column): Column collect_set(columnName: String): Column

| corr a| [[corr]]

[source, scala]

corr(column1: Column, column2: Column): Column corr(columnName1: String, columnName2: String): Column

| count a| [[count]]

[source, scala]

count(e: Column): Column count(columnName: String): TypedColumn[Any, Long]

| countDistinct a| [[countDistinct]]

[source, scala]

countDistinct(expr: Column, exprs: Column*): Column countDistinct(columnName: String, columnNames: String*): Column

| covar_pop a| [[covar_pop]]

[source, scala]

covar_pop(column1: Column, column2: Column): Column covar_pop(columnName1: String, columnName2: String): Column

| covar_samp a| [[covar_samp]]

[source, scala]

covar_samp(column1: Column, column2: Column): Column covar_samp(columnName1: String, columnName2: String): Column

| first a| [[first]]

[source, scala]

first(e: Column): Column first(e: Column, ignoreNulls: Boolean): Column first(columnName: String): Column first(columnName: String, ignoreNulls: Boolean): Column

Returns the first value in a group. Returns the first non-null value when ignoreNulls flag on. If all values are null, then returns null.

| grouping a| [[grouping]]

[source, scala]

grouping(e: Column): Column grouping(columnName: String): Column

Indicates whether a given column is aggregated or not

| grouping_id a| [[grouping_id]]

[source, scala]

grouping_id(cols: Column*): Column grouping_id(colName: String, colNames: String*): Column

Computes the level of grouping

| kurtosis a| [[kurtosis]]

[source, scala]

kurtosis(e: Column): Column kurtosis(columnName: String): Column

| last a| [[last]]

[source, scala]

last(e: Column, ignoreNulls: Boolean): Column last(columnName: String, ignoreNulls: Boolean): Column last(e: Column): Column last(columnName: String): Column

| max a| [[max]]

[source, scala]

max(e: Column): Column max(columnName: String): Column

| mean a| [[mean]]

[source, scala]

mean(e: Column): Column mean(columnName: String): Column

| min a| [[min]]

[source, scala]

min(e: Column): Column min(columnName: String): Column

| skewness a| [[skewness]]

[source, scala]

skewness(e: Column): Column skewness(columnName: String): Column

| stddev a| [[stddev]]

[source, scala]

stddev(e: Column): Column stddev(columnName: String): Column

| stddev_pop a| [[stddev_pop]]

[source, scala]

stddev_pop(e: Column): Column stddev_pop(columnName: String): Column

| stddev_samp a| [[stddev_samp]]

[source, scala]

stddev_samp(e: Column): Column stddev_samp(columnName: String): Column

| sum a| [[sum]]

[source, scala]

sum(e: Column): Column sum(columnName: String): Column

| sumDistinct a| [[sumDistinct]]

[source, scala]

sumDistinct(e: Column): Column sumDistinct(columnName: String): Column

| variance a| [[variance]]

[source, scala]

variance(e: Column): Column variance(columnName: String): Column

| var_pop a| [[var_pop]]

[source, scala]

var_pop(e: Column): Column var_pop(columnName: String): Column

| var_samp a| [[var_samp]]

[source, scala]

var_samp(e: Column): Column var_samp(columnName: String): Column

|===

=== [[grouping]] grouping Aggregate Function

[source, scala]

grouping(e: Column): Column grouping(columnName: String): Column // <1>

<1> Calls the first grouping with columnName as a Column

grouping is an aggregate function that indicates whether a specified column is aggregated or not and:

  • returns 1 if the column is in a subtotal and is NULL
  • returns 0 if the underlying value is NULL or any other value

NOTE: grouping can only be used with spark-sql-multi-dimensional-aggregation.md#cube[cube], spark-sql-multi-dimensional-aggregation.md#rollup[rollup] or GROUPING SETS multi-dimensional aggregate operators (and is verified when CheckAnalysis.md#Grouping[Analyzer does check analysis]).

From Hive's documentation about Grouping__ID function (that can somehow help to understand grouping):

When aggregates are displayed for a column its value is null. This may conflict in case the column itself has some null values. There needs to be some way to identify NULL in column, which means aggregate and NULL in column, which means value. GROUPING__ID function is the solution to that.

val tmpWorkshops = Seq(
  ("Warsaw", 2016, 2),
  ("Toronto", 2016, 4),
  ("Toronto", 2017, 1)).toDF("city", "year", "count")

// there seems to be a bug with nulls
// and so the need for the following union
val cityNull = Seq(
  (null.asInstanceOf[String], 2016, 2)).toDF("city", "year", "count")

val workshops = tmpWorkshops union cityNull

scala> workshops.show
+-------+----+-----+
|   city|year|count|
+-------+----+-----+
| Warsaw|2016|    2|
|Toronto|2016|    4|
|Toronto|2017|    1|
|   null|2016|    2|
+-------+----+-----+

val q = workshops
  .cube("city", "year")
  .agg(grouping("city"), grouping("year")) // <-- grouping here
  .sort($"city".desc_nulls_last, $"year".desc_nulls_last)

scala> q.show
+-------+----+--------------+--------------+
|   city|year|grouping(city)|grouping(year)|
+-------+----+--------------+--------------+
| Warsaw|2016|             0|             0|
| Warsaw|null|             0|             1|
|Toronto|2017|             0|             0|
|Toronto|2016|             0|             0|
|Toronto|null|             0|             1|
|   null|2017|             1|             0|
|   null|2016|             1|             0|
|   null|2016|             0|             0|  <-- null is city
|   null|null|             0|             1|  <-- null is city
|   null|null|             1|             1|
+-------+----+--------------+--------------+

Internally, grouping creates a Column with Grouping expression.

val q = workshops.cube("city", "year").agg(grouping("city"))
scala> println(q.queryExecution.logical)
'Aggregate [cube(city#182, year#183)], [city#182, year#183, grouping('city) AS grouping(city)#705]
+- Union
   :- Project [_1#178 AS city#182, _2#179 AS year#183, _3#180 AS count#184]
   :  +- LocalRelation [_1#178, _2#179, _3#180]
   +- Project [_1#192 AS city#196, _2#193 AS year#197, _3#194 AS count#198]
      +- LocalRelation [_1#192, _2#193, _3#194]

scala> println(q.queryExecution.analyzed)
Aggregate [city#724, year#725, spark_grouping_id#721], [city#724, year#725, cast((shiftright(spark_grouping_id#721, 1) & 1) as tinyint) AS grouping(city)#720]
+- Expand [List(city#182, year#183, count#184, city#722, year#723, 0), List(city#182, year#183, count#184, city#722, null, 1), List(city#182, year#183, count#184, null, year#723, 2), List(city#182, year#183, count#184, null, null, 3)], [city#182, year#183, count#184, city#724, year#725, spark_grouping_id#721]
   +- Project [city#182, year#183, count#184, city#182 AS city#722, year#183 AS year#723]
      +- Union
         :- Project [_1#178 AS city#182, _2#179 AS year#183, _3#180 AS count#184]
         :  +- LocalRelation [_1#178, _2#179, _3#180]
         +- Project [_1#192 AS city#196, _2#193 AS year#197, _3#194 AS count#198]
            +- LocalRelation [_1#192, _2#193, _3#194]

NOTE: grouping was added to Spark SQL in https://issues.apache.org/jira/browse/SPARK-12706[[SPARK-12706] support grouping/grouping_id function together group set].

=== [[grouping_id]] grouping_id Aggregate Function

[source, scala]

grouping_id(cols: Column*): Column grouping_id(colName: String, colNames: String*): Column // <1>

<1> Calls the first grouping_id with colName and colNames as objects of type Column

grouping_id is an aggregate function that computes the level of grouping:

  • 0 for combinations of each column
  • 1 for subtotals of column 1
  • 2 for subtotals of column 2
  • And so on…

[source, scala]

val tmpWorkshops = Seq( ("Warsaw", 2016, 2), ("Toronto", 2016, 4), ("Toronto", 2017, 1)).toDF("city", "year", "count")

// there seems to be a bug with nulls // and so the need for the following union val cityNull = Seq( (null.asInstanceOf[String], 2016, 2)).toDF("city", "year", "count")

val workshops = tmpWorkshops union cityNull

scala> workshops.show +-------+----+-----+ | city|year|count| +-------+----+-----+ | Warsaw|2016| 2| |Toronto|2016| 4| |Toronto|2017| 1| | null|2016| 2| +-------+----+-----+

val query = workshops .cube("city", "year") .agg(grouping_id()) // ← all grouping columns used .sort($"city".desc_nulls_last, $"year".desc_nulls_last) scala> query.show +-------+----+-------------+ | city|year|grouping_id()| +-------+----+-------------+ | Warsaw|2016| 0| | Warsaw|null| 1| |Toronto|2017| 0| |Toronto|2016| 0| |Toronto|null| 1| | null|2017| 2| | null|2016| 2| | null|2016| 0| | null|null| 1| | null|null| 3| +-------+----+-------------+

scala> spark.catalog.listFunctions.filter(_.name.contains("grouping_id")).show(false) +-----------+--------+-----------+----------------------------------------------------+-----------+ |name |database|description|className |isTemporary| +-----------+--------+-----------+----------------------------------------------------+-----------+ |grouping_id|null |null |org.apache.spark.sql.catalyst.expressions.GroupingID|true | +-----------+--------+-----------+----------------------------------------------------+-----------+

// bin function gives the string representation of the binary value of the given long column scala> query.withColumn("bitmask", bin($"grouping_id()")).show +-------+----+-------------+-------+ | city|year|grouping_id()|bitmask| +-------+----+-------------+-------+ | Warsaw|2016| 0| 0| | Warsaw|null| 1| 1| |Toronto|2017| 0| 0| |Toronto|2016| 0| 0| |Toronto|null| 1| 1| | null|2017| 2| 10| | null|2016| 2| 10| | null|2016| 0| 0| ← null is city | null|null| 3| 11| | null|null| 1| 1| +-------+----+-------------+-------+

The list of columns of grouping_id should match grouping columns (in cube or rollup) exactly, or empty which means all the grouping columns (which is exactly what the function expects).

NOTE: grouping_id can only be used with spark-sql-multi-dimensional-aggregation.md#cube[cube], spark-sql-multi-dimensional-aggregation.md#rollup[rollup] or GROUPING SETS multi-dimensional aggregate operators (and is verified when CheckAnalysis.md#GroupingID[Analyzer does check analysis]).

NOTE: Spark SQL's grouping_id function is known as grouping__id in Hive.

From Hive's documentation about Grouping__ID function:

When aggregates are displayed for a column its value is null. This may conflict in case the column itself has some null values. There needs to be some way to identify NULL in column, which means aggregate and NULL in column, which means value. GROUPING__ID function is the solution to that.

Internally, grouping_id() creates a Column with GroupingID unevaluable expression.

// workshops dataset was defined earlier
val q = workshops
  .cube("city", "year")
  .agg(grouping_id())

// grouping_id function is spark_grouping_id virtual column internally
// that is resolved during analysis - see Analyzed Logical Plan
scala> q.explain(true)
== Parsed Logical Plan ==
'Aggregate [cube(city#182, year#183)], [city#182, year#183, grouping_id() AS grouping_id()#742]
+- Union
   :- Project [_1#178 AS city#182, _2#179 AS year#183, _3#180 AS count#184]
   :  +- LocalRelation [_1#178, _2#179, _3#180]
   +- Project [_1#192 AS city#196, _2#193 AS year#197, _3#194 AS count#198]
      +- LocalRelation [_1#192, _2#193, _3#194]

== Analyzed Logical Plan ==
city: string, year: int, grouping_id(): int
Aggregate [city#757, year#758, spark_grouping_id#754], [city#757, year#758, spark_grouping_id#754 AS grouping_id()#742]
+- Expand [List(city#182, year#183, count#184, city#755, year#756, 0), List(city#182, year#183, count#184, city#755, null, 1), List(city#182, year#183, count#184, null, year#756, 2), List(city#182, year#183, count#184, null, null, 3)], [city#182, year#183, count#184, city#757, year#758, spark_grouping_id#754]
   +- Project [city#182, year#183, count#184, city#182 AS city#755, year#183 AS year#756]
      +- Union
         :- Project [_1#178 AS city#182, _2#179 AS year#183, _3#180 AS count#184]
         :  +- LocalRelation [_1#178, _2#179, _3#180]
         +- Project [_1#192 AS city#196, _2#193 AS year#197, _3#194 AS count#198]
            +- LocalRelation [_1#192, _2#193, _3#194]

== Optimized Logical Plan ==
Aggregate [city#757, year#758, spark_grouping_id#754], [city#757, year#758, spark_grouping_id#754 AS grouping_id()#742]
+- Expand [List(city#755, year#756, 0), List(city#755, null, 1), List(null, year#756, 2), List(null, null, 3)], [city#757, year#758, spark_grouping_id#754]
   +- Union
      :- LocalRelation [city#755, year#756]
      +- LocalRelation [city#755, year#756]

== Physical Plan ==
*HashAggregate(keys=[city#757, year#758, spark_grouping_id#754], functions=[], output=[city#757, year#758, grouping_id()#742])
+- Exchange hashpartitioning(city#757, year#758, spark_grouping_id#754, 200)
   +- *HashAggregate(keys=[city#757, year#758, spark_grouping_id#754], functions=[], output=[city#757, year#758, spark_grouping_id#754])
      +- *Expand [List(city#755, year#756, 0), List(city#755, null, 1), List(null, year#756, 2), List(null, null, 3)], [city#757, year#758, spark_grouping_id#754]
         +- Union
            :- LocalTableScan [city#755, year#756]
            +- LocalTableScan [city#755, year#756]

NOTE: grouping_id was added to Spark SQL in https://issues.apache.org/jira/browse/SPARK-12706[[SPARK-12706] support grouping/grouping_id function together group set].

Last update: 2021-02-18
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