PySpark for Large Data

pip install pyspark
# or use Databricks Community Edition (free)

from pyspark.sql import SparkSession
from pyspark.sql import functions as F
from pyspark.sql.types import StructType, StructField, StringType, DoubleType, DateType

spark = SparkSession.builder \
    .appName('SalesAnalysis') \
    .master('local[*]') \
    .getOrCreate()

# Read CSV with schema inference
df = spark.read.csv('sales.csv', header=True, inferSchema=True)
df.printSchema()
df.show(5)

# DataFrame transformations (lazy — nothing runs until an action)
result = (
    df
    .filter(F.col('status') == 'completed')
    .withColumn('revenue', F.col('quantity') * F.col('unit_price'))
    .withColumn('month', F.month('order_date'))
    .groupBy('month', 'category')
    .agg(
        F.sum('revenue').alias('total_revenue'),
        F.count('*').alias('order_count'),
        F.avg('revenue').alias('avg_order_value'),
    )
    .orderBy('month', F.desc('total_revenue'))
)

# Action — triggers execution
result.show()

# Write to Parquet (columnar, compressed, fast)
result.write.mode('overwrite').parquet('output/monthly_revenue/')

spark.stop()

# Window functions in Spark
from pyspark.sql.window import Window

window = Window.partitionBy('customer_id').orderBy('order_date')

ranked = df.withColumn(
    'order_rank', F.row_number().over(window)
).withColumn(
    'running_total', F.sum('revenue').over(window)
)