reduce

Applies a binary operator to an initial state and all elements in the array, and reduces this to a single state. The final state is converted into the final result by applying a finish function.

For the corresponding Databricks SQL function, see reduce function.

Syntax

from pyspark.databricks.sql import functions as dbf

dbf.reduce(col=<col>, initialValue=<initialValue>, merge=<merge>, finish=<finish>)

Parameters

Parameter	Type	Description
col	pyspark.sql.Column or str	Name of column or expression.
initialValue	pyspark.sql.Column or str	Initial value. Name of column or expression.
merge	function	A binary function that returns expression of the same type as zero.
finish	function, optional	An optional unary function used to convert accumulated value.

Returns

pyspark.sql.Column: final value after aggregate function is applied.

Examples

Example 1: Simple reduction with sum

from pyspark.databricks.sql import functions as dbf
df = spark.createDataFrame([(1, [20.0, 4.0, 2.0, 6.0, 10.0])], ("id", "values"))
df.select(dbf.reduce("values", dbf.lit(0.0), lambda acc, x: acc + x).alias("sum")).show()

+----+
| sum|
+----+
|42.0|
+----+

Example 2: Reduction with finish function

from pyspark.databricks.sql import functions as dbf
df = spark.createDataFrame([(1, [20.0, 4.0, 2.0, 6.0, 10.0])], ("id", "values"))
def merge(acc, x):
    count = acc.count + 1
    sum = acc.sum + x
    return dbf.struct(count.alias("count"), sum.alias("sum"))
df.select(
    dbf.reduce(
        "values",
        dbf.struct(dbf.lit(0).alias("count"), dbf.lit(0.0).alias("sum")),
        merge,
        lambda acc: acc.sum / acc.count,
    ).alias("mean")
).show()

+----+
|mean|
+----+
| 8.4|
+----+