CODEWITHSUNDEEP
pythongroup-bypyspark
Manu Sharma
Manu Sharma

Reputation: 1739

Groupby operations on multiple columns Pyspark

I have applied a groupby and calculating the standard deviation for two features in pyspark dataframe

from pyspark.sql import functions as f


val1 = [('a',20,100),('a',100,100),('a',50,100),('b',0,100),('b',0,100),('c',0,0),('c',0,50),('c',0,100),('c',0,20)]
cols = ['group','val1','val2']
tf = spark.createDataFrame(val1, cols)
tf.show() 
tf.groupby('group').agg(f.stddev(['val1','val2']).alias('val1_std','val2_std'))

but it is giving me following error 

TypeError: _() takes 1 positional argument but 2 were given

How to perform it in pyspark?

Upvotes: 0

Views: 539

Answers (1)

ags29
ags29

Reputation: 2696

The problem is that the stddev function acts on a single column rather than multiple columns as in the code you have written (hence the error message about 1 vs 2 arguments). One way to get what you are looking for is to calculate the standard deviation separately for each column:

# std dev for each col
expressions = [f.stddev(col).alias('%s_std'%(col)) for col in ['val1','val2']]
# Now run it
tf.groupby('group').agg(*expressions).show()

#+-----+------------------+------------------+
#|group|          val1_std|          val2_std|
#+-----+------------------+------------------+
#|    c|               0.0|43.493294502332965|
#|    b|               0.0|               0.0|
#|    a|40.414518843273804|               0.0|
#+-----+------------------+------------------+

Upvotes: 1

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