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Returns the first value of col for a group of rows. It will return the first non-null value it sees when ignoreNulls is set to true. If all values are null, then null is returned.
Syntax
from pyspark.sql import functions as sf
sf.first_value(col, ignoreNulls=None)
Parameters
| Parameter | Type | Description |
|---|---|---|
col |
pyspark.sql.Column or str |
Target column to work on. |
ignoreNulls |
pyspark.sql.Column or bool, optional |
If first value is null then look for first non-null value. |
Returns
pyspark.sql.Column: some value of col for a group of rows.
Examples
Example 1: Get first value without ignoring nulls
from pyspark.sql import functions as sf
spark.createDataFrame(
[(None, 1), ("a", 2), ("a", 3), ("b", 8), ("b", 2)], ["a", "b"]
).select(sf.first_value('a'), sf.first_value('b')).show()
+--------------+--------------+
|first_value(a)|first_value(b)|
+--------------+--------------+
| NULL| 1|
+--------------+--------------+
Example 2: Get first value ignoring nulls
from pyspark.sql import functions as sf
spark.createDataFrame(
[(None, 1), ("a", 2), ("a", 3), ("b", 8), ("b", 2)], ["a", "b"]
).select(sf.first_value('a', True), sf.first_value('b', True)).show()
+--------------+--------------+
|first_value(a)|first_value(b)|
+--------------+--------------+
| a| 1|
+--------------+--------------+