Using LEAD or LAG¶

Let us understand the usage of LEAD or LAG functions. Both are used for similar scenarios.

Let us start spark context for this Notebook so that we can execute the code provided. You can sign up for our 10 node state of the art cluster/labs to learn Spark SQL using our unique integrated LMS.

from pyspark.sql import SparkSession

import getpass
username = getpass.getuser()

spark = SparkSession. \
    builder. \
    config('spark.ui.port', '0'). \
    config("spark.sql.warehouse.dir", f"/user/{username}/warehouse"). \
    enableHiveSupport(). \
    appName(f'{username} | Python - Windowing Functions'). \
    master('yarn'). \
    getOrCreate()

If you are going to use CLIs, you can use Spark SQL using one of the 3 approaches.

Using Spark SQL

spark2-sql \
    --master yarn \
    --conf spark.ui.port=0 \
    --conf spark.sql.warehouse.dir=/user/${USER}/warehouse

Using Scala

spark2-shell \
    --master yarn \
    --conf spark.ui.port=0 \
    --conf spark.sql.warehouse.dir=/user/${USER}/warehouse

Using Pyspark

pyspark2 \
    --master yarn \
    --conf spark.ui.port=0 \
    --conf spark.sql.warehouse.dir=/user/${USER}/warehouse

spark.conf.set('spark.sql.shuffle.partitions', '2')

airtraffic_path = "/public/airtraffic_all/airtraffic-part/flightmonth=200801"

airtraffic = spark. \
  read. \
  parquet(airtraffic_path)

from pyspark.sql.functions import col, lit, lpad, concat

from pyspark.sql.functions import lead

from pyspark.sql.window import Window

spec = Window. \
    partitionBy("FlightDate", "Origin"). \
    orderBy(col("CRSDepTime"))

airtraffic. \
    filter("IsDepDelayed = 'YES' and Cancelled = 0"). \
    select(concat("Year", 
                  lpad("Month", 2, "0"), 
                  lpad("DayOfMonth", 2, "0")
                 ).alias("FlightDate"),
           "Origin",
           "UniqueCarrier",
           "FlightNum",
           "CRSDepTime",
           "IsDepDelayed",
           col("DepDelay").cast("int").alias("DepDelay")
          ). \
    withColumn("LeadUniqueCarrier", lead("UniqueCarrier").over(spec)). \
    withColumn("LeadFlightNum", lead("FlightNum").over(spec)). \
    withColumn("LeadCRSDepTime", lead("CRSDepTime").over(spec)). \
    withColumn("LeadDepDelay", lead("DepDelay").over(spec)). \
    orderBy("FlightDate", "Origin", "CRSDepTime"). \
    show()

Using LEAD or LAG with 7¶

airtraffic_path = "/public/airtraffic_all/airtraffic-part/flightmonth=200801"

airtraffic = spark. \
    read. \
    parquet(airtraffic_path)

from pyspark.sql.functions import col, lit, lpad, concat

from pyspark.sql.functions import sum, lead, substring

from pyspark.sql.window import Window

spec = Window. \
    partitionBy(substring("FlightDate", 1, 6), "Origin"). \
    orderBy("FlightDate", col("TotalDepDelay").desc())

airtraffic. \
    filter("""IsDepDelayed = 'YES' 
              AND Cancelled = 0
              AND concat(Year, 
                         lpad(Month, 2, '0'),
                         lpad(DayOfMonth, 2, '0')
                        ) BETWEEN 20080101 AND 20080114
              AND Origin IN ('ATL', 'DFW', 'JFK', 'LAX', 'SFO', 'ORD')
           """
          ). \
    groupBy(concat("Year", 
                   lpad("Month", 2, "0"), 
                   lpad("DayOfMonth", 2, "0")
                  ).alias("FlightDate"), 
            "Origin"
           ). \
    agg(sum(col("DepDelay").cast("int")).alias("TotalDepDelay")). \
    withColumn("LeadFlightDate", lead("FlightDate", 7).over(spec)). \
    withColumn("LeadOrigin", lead("Origin", 7).over(spec)). \
    withColumn("LeadTotalDepDelay", lead("TotalDepDelay", 7).over(spec)). \
    filter('Origin = "ORD"'). \
    orderBy("FlightDate", col("TotalDepDelay").desc()). \
    show()

airtraffic. \
    filter("""IsDepDelayed = 'YES' 
              AND Cancelled = 0
              AND concat(Year, 
                         lpad(Month, 2, '0'),
                         lpad(DayOfMonth, 2, '0')
                        ) BETWEEN 20080101 AND 20080114
              AND Origin IN ('ATL', 'DFW', 'JFK', 'LAX', 'SFO', 'ORD')
           """
          ). \
    groupBy(concat("Year", 
                   lpad("Month", 2, "0"), 
                   lpad("DayOfMonth", 2, "0")
                  ).alias("FlightDate"), 
            "Origin"
           ). \
    agg(sum(col("DepDelay").cast("int")).alias("TotalDepDelay")). \
    withColumn("LeadFlightDate", lead("FlightDate", 7).over(spec)). \
    withColumn("LeadOrigin", lead("Origin", 7).over(spec)). \
    withColumn("LeadTotalDepDelay", lead("TotalDepDelay", 7).over(spec)). \
    filter('Origin = "ORD" AND FlightDate BETWEEN 20080101 AND 20080107'). \
    orderBy("FlightDate", col("TotalDepDelay").desc()). \
    show()

airtraffic. \
    filter("""IsDepDelayed = 'YES' 
              AND Cancelled = 0
              AND concat(Year, 
                         lpad(Month, 2, '0'),
                         lpad(DayOfMonth, 2, '0')
                        ) BETWEEN 20080101 AND 20080114
              AND Origin IN ('ATL', 'DFW', 'JFK', 'LAX', 'SFO', 'ORD')
           """
          ). \
    groupBy(concat("Year", 
                   lpad("Month", 2, "0"), 
                   lpad("DayOfMonth", 2, "0")
                  ).alias("FlightDate"), 
            "Origin"
           ). \
    agg(sum(col("DepDelay").cast("int")).alias("TotalDepDelay")). \
    withColumn("LeadFlightDate", lead("FlightDate", 7).over(spec)). \
    withColumn("LeadOrigin", lead("Origin", 7).over(spec)). \
    withColumn("LeadTotalDepDelay", lead("TotalDepDelay", 7).over(spec)). \
    filter('FlightDate BETWEEN 20080101 AND 20080107'). \
    orderBy("FlightDate", col("TotalDepDelay").desc()). \
    show()

Mastering Pyspark

Using LEAD or LAG¶

Using LEAD or LAG with 7¶