Spark sql top n per group

apache-spark group-by apache-spark-sql top-n
Georg Heiler picture Georg Heiler · Apr 16, 2016 · Viewed 9.9k times · Source

How can I get the top-n (lets say top 10 or top 3) per group in spark-sql?

http://www.xaprb.com/blog/2006/12/07/how-to-select-the-firstleastmax-row-per-group-in-sql/ provides a tutorial for general SQL. However, spark does not implement subqueries in the where clause.

Answer

tyagi picture tyagi · Apr 16, 2016

You can use the window function feature that was added in Spark 1.4 Suppose that we have a productRevenue table as shown below. enter image description here

the answer to What are the best-selling and the second best-selling products in every category is as follows

SELECT product,category,revenue FROM 
   (SELECT product,category,revenue,dense_rank() 
         OVER (PARTITION BY category ORDER BY revenue DESC) as rank 
    FROM productRevenue) tmp 
WHERE rank <= 2

Tis will give you the desired result

Related questions

How can I change column types in Spark SQL's DataFrame?

Suppose I'm doing something like: val df = sqlContext.load("com.databricks.spark.csv", Map("path" -> "cars.csv", "header" -> "true")) df.printSchema() root |-- year: string (nullable = true) |-- make: string (nullable = true) |-- model: string (nullable = …

Read More
Spark - load CSV file as DataFrame?

I would like to read a CSV in spark and convert it as DataFrame and store it in HDFS with df.registerTempTable("table_name") I have tried: scala> val df = sqlContext.load("hdfs:///csv/file/dir/file.csv") Error …

Read More
How to change dataframe column names in pyspark?

I come from pandas background and am used to reading data from CSV files into a dataframe and then simply changing the column names to something useful using the simple command: df.columns = new_column_name_list However, the same …

Read More