[Spark By Example] Spark SQL – Grouping

Let’s play with Spark SQL more.

[Note] When the underlying DataFrame schema is changed, the view should be updated again.


Data File

  • Create a csv file with the following content.
first name,last name,age
Paul,Henderson,20
Grace,Carr,32
Julia,Jackson,14
Alexandra,May,43
Anna,Jones,24

Result


Python Application

from pyspark.sql import SparkSession
from pyspark.sql.types import *
from pyspark.sql.functions import *

if __name__ == "__main__":

  spark = (SparkSession
        .builder
        .appName("people-sql-group")
        .getOrCreate())

  data_file = "test/data/people.csv"

  # schema
  custom_schema = StructType([
        StructField("first name", StringType(), False),
        StructField("last name", StringType(), False),
        StructField("age", IntegerType(), False)])

  data_df = (spark.read.format("csv")
          .option("header", True)
          .schema(custom_schema)
          .load(data_file))
  data_df = (data_df
      .withColumnRenamed("first name", "firstname")
      .withColumnRenamed("last name", "lastname"))

  # create a view
  data_df.createOrReplaceTempView("people_view")

  # spark sql - projection
  query = """SELECT firstname, lastname, age
        FROM people_view
  """
  spark.sql(query).show()

  # add a new column to the dataframe
  data_df = data_df.withColumn("ageGroup", floor(col("age")/10)*10)

  # the following query will fail 
  # the view does not have a new column
  query = "SELECT ageGroup FROM people_view"
  #spark.sql(query).show()

  # need to replace the view
  data_df.createOrReplaceTempView("people_view")
  spark.sql(query).show()

  # spark sql - grouping
  query = """SELECT ageGroup, COUNT(*) AS count 
        FROM people_view
        GROUP BY ageGroup
        ORDER BY ageGroup DESC
  """
  spark.sql(query).show()

  spark.stop()

C# Application

using Microsoft.Spark.Sql;
using Microsoft.Spark.Sql.Types;
using static Microsoft.Spark.Sql.Functions;

namespace MySpark.Examples
{
    internal class PeopleSqlGrouping
    {
        public static void Run()
        {
            SparkSession spark =
                SparkSession
                    .Builder()
                    .AppName("column-test")
                    .GetOrCreate();

            string filePath = "data/people.csv";

            // schema
            StructField[] fields = {
                new StructField("first name", new StringType(), false),
                new StructField("last name", new StringType(), false),
                new StructField("age", new IntegerType(), false)
            };
            StructType schema = new StructType(fields);

            // initial data frame
            DataFrame dataDF = spark.Read()
                .Format("csv")
                .Option("header", true)
                .Schema(schema)
                .Load(filePath);
            dataDF = dataDF
                .WithColumnRenamed("first name", "firstname")
                .WithColumnRenamed("last name", "lastname");

            // create a view
            dataDF.CreateOrReplaceTempView("people_view");

            // spark sql - projection
            string query = @"
                SELECT firstname, lastname, age
                FROM people_view";
            spark.Sql(query).Show();

            // # add a new column to the dataframe
            dataDF = dataDF.WithColumn(
                "ageGroup",
                Floor(Col("age") / 10) * 10);

            // the following query will fail 
            // the view does not have a new column
            query = "SELECT ageGroup FROM people_view";
            // spark.Sql(query).Show();

            // need to replace the view
            dataDF.CreateOrReplaceTempView("people_view");
            spark.Sql(query).Show();

            // spark sql - grouping
            query = @"
                SELECT ageGroup, COUNT(*) AS count 
                FROM people_view
                GROUP BY ageGroup
                ORDER BY ageGroup DESC";
            spark.Sql(query).Show();

            spark.Stop();
        }
    }
}

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