lead

Window function: returns the value that is offset rows after the current row, and default if there is less than offset rows after the current row. For example, an offset of one will return the next row at any given point in the window partition.

This is equivalent to the LEAD function in SQL.

Syntax

from pyspark.sql import functions as sf

sf.lead(col, offset=1, default=None)

Parameters

Parameter	Type	Description
col	pyspark.sql.Column or column name	Name of column or expression.
offset	int, optional	Number of row to extend. Default is 1.
default	optional	Default value.

Returns

pyspark.sql.Column: value after current row based on offset.

Examples

Example 1: Using lead to get next value

from pyspark.sql import functions as sf
from pyspark.sql import Window
df = spark.createDataFrame(
    [("a", 1), ("a", 2), ("a", 3), ("b", 8), ("b", 2)], ["c1", "c2"])
df.show()

+---+---+
| c1| c2|
+---+---+
|  a|  1|
|  a|  2|
|  a|  3|
|  b|  8|
|  b|  2|
+---+---+

w = Window.partitionBy("c1").orderBy("c2")
df.withColumn("next_value", sf.lead("c2").over(w)).show()

+---+---+----------+
| c1| c2|next_value|
+---+---+----------+
|  a|  1|         2|
|  a|  2|         3|
|  a|  3|      NULL|
|  b|  2|         8|
|  b|  8|      NULL|
+---+---+----------+

Example 2: Using lead with a default value

from pyspark.sql import functions as sf
from pyspark.sql import Window
df = spark.createDataFrame(
    [("a", 1), ("a", 2), ("a", 3), ("b", 8), ("b", 2)], ["c1", "c2"])
w = Window.partitionBy("c1").orderBy("c2")
df.withColumn("next_value", sf.lead("c2", 1, 0).over(w)).show()

+---+---+----------+
| c1| c2|next_value|
+---+---+----------+
|  a|  1|         2|
|  a|  2|         3|
|  a|  3|         0|
|  b|  2|         8|
|  b|  8|         0|
+---+---+----------+

Example 3: Using lead with an offset of 2

from pyspark.sql import functions as sf
from pyspark.sql import Window
df = spark.createDataFrame(
    [("a", 1), ("a", 2), ("a", 3), ("b", 8), ("b", 2)], ["c1", "c2"])
w = Window.partitionBy("c1").orderBy("c2")
df.withColumn("next_value", sf.lead("c2", 2, -1).over(w)).show()

+---+---+----------+
| c1| c2|next_value|
+---+---+----------+
|  a|  1|         3|
|  a|  2|        -1|
|  a|  3|        -1|
|  b|  2|        -1|
|  b|  8|        -1|
+---+---+----------+