Column alias after groupBy in pyspark

Question

I need the resulting data frame in the line below, to have an alias name “maxDiff” for the max(‘diff’) column after groupBy. However, the below line does not makeany change, nor throw an error.

 grpdf = joined_df.groupBy(temp1.datestamp).max('diff').alias("maxDiff")

Asked By: mhn

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Source

Answer 1

This is because you are aliasing the whole DataFrame object, not Column. Here’s an example how to alias the Column only:

import pyspark.sql.functions as func

grpdf = joined_df 
    .groupBy(temp1.datestamp) 
    .max('diff') 
    .select(func.col("max(diff)").alias("maxDiff"))

Answered By: Nhor

Answer 2

You can use agg instead of calling max method:

from pyspark.sql.functions import max

joined_df.groupBy(temp1.datestamp).agg(max("diff").alias("maxDiff"))

Similarly in Scala

import org.apache.spark.sql.functions.max

joined_df.groupBy($"datestamp").agg(max("diff").alias("maxDiff"))

or

joined_df.groupBy($"datestamp").agg(max("diff").as("maxDiff"))

Answered By: zero323

Answer 3

In addition to the answers already here, the following are also convenient ways if you know the name of the aggregated column, where you don’t have to import from pyspark.sql.functions:

1

grouped_df = joined_df.groupBy(temp1.datestamp) 
                      .max('diff') 
                      .selectExpr('max(diff) AS maxDiff')

See docs for info on .selectExpr()

2

grouped_df = joined_df.groupBy(temp1.datestamp) 
                      .max('diff') 
                      .withColumnRenamed('max(diff)', 'maxDiff')

See docs for info on .withColumnRenamed()

This answer here goes into more detail: https://stackoverflow.com/a/34077809

Answered By: vk1011

Answer 4

you can use.

grouped_df = grpdf.select(col("max(diff)") as "maxdiff",col("sum(DIFF)") as "sumdiff").show()

Answered By: Nilay Bhardwaj

Column alias after groupBy in pyspark

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