CODEWITHSUNDEEP
pythonapache-sparkpysparkapache-spark-sql
Satya
Satya

Reputation: 5917

python+pyspark: error on inner join with multiple column comparison in pyspark

Hi I have 2 dataframes to join

#df1
 name    genre  count
 satya   drama    1
 satya   action   3
 abc     drame    2
 abc     comedy   2
 def     romance  1

#df2
 name  max_count
 satya  3
 abc    2
 def    1

Now I want to join above 2 dfs on name and count==max_count, But i am getting an error

import pyspark.sql.functions as F
from pyspark.sql.functions import count, col
from pyspark.sql.functions import struct
df = spark.read.csv('file',sep = '###', header=True)
df1 = df.groupBy("name", "genre").count()
df2 = df1.groupby('name').agg(F.max("count").alias("max_count"))
#Now trying to join both dataframes
final_df = df1.join(df2, (df1.name == df2.name) & (df1.count == df2.max_count))
final_df.show() ###Error
#py4j.protocol.Py4JJavaError: An error occurred while calling o207.showString.
: org.apache.spark.SparkException: Exception thrown in awaitResult:
    at org.apache.spark.util.ThreadUtils$.awaitResult(ThreadUtils.scala:194)
#Caused by: java.lang.UnsupportedOperationException: Cannot evaluate expression: count(1)
    at org.apache.spark.sql.catalyst.expressions.Unevaluable$class.doGenCode(Expression.scala:224)

But success with "left " join

final_df = df1.join(df2, (df1.name == df2.name) & (df1.count == df2.max_count), "left")
final_df.show()  ###Success but i don't want left join , i want inner join

My question is why the above one fails, am I doing something wrong there???

I referred this link "Find maximum row per group in Spark DataFrame". Used the first answer (2 groupby method).But same error.

I am on spark-2.0.0-bin-hadoop2.7 and python 2.7.

Please suggest.Thanks.

Edit:

The above scenario works with spark 1.6 (which is quite surprising that what's wrong with spark 2.0 (or with my installation , I will reinstall, check and update here)).

Has anybody tried this on spark 2.0 and got success , by following Yaron's answer below???

Upvotes: 0

Views: 10109

Answers (3)

user6891234
user6891234

Reputation: 31

I ran into the same problem when I tried to join two DataFrames where one of them was GroupedData. It worked for me when I cached the GroupedData DataFrame before the inner join. For your code, try:

df1 = df.groupBy("name", "genre").count().cache()    # added cache()
df2 = df1.groupby('name').agg(F.max("count").alias("max_count")).cache()   # added cache()
final_df = df1.join(df2, (df1.name == df2.name) & (df1.count == df2.max_count))    # no change

Upvotes: 3

Satya
Satya

Reputation: 5917

My work-around in spark 2.0

I created a single column('combined') from columns in join comparision('name','mycount')in respective dfs, so now I have one column to compare and this is not creating any issue as I am comparing only one column.

def combine_func(*args):
  data = '_'.join([str(x) for x in args]) ###converting nonstring to str tehn concatenation
  return data
combine_func = udf(combine_func, StringType())  ##register the func as udf
df1 = df1.withColumn('combined_new_1', combine_new(df1['name'],df1['mycount']))  ###a col having concatenated value from name and mycount columns eg: 'satya_3'
df2 = df2.withColumn('combined_new_2', combine_new(df2['name2'],df2['max_count']))
#df1.columns == 'name','genre', 'mycount', 'combined_new_1'
#df2.columns == 'name2', 'max_count', 'combined_new_2'
#Now join 
final_df = df1.join(df2,df1.combined_new_1 == df2.combined_new_2, 'inner')
#final_df = df1.join(df2,df1.combined_new_1 == df2.combined_new_2, 'inner').select('the columns you want')
final_df.show()  ####It is showing the result, Trust me.

Please don't follow until unless you are in a hurry, Better search for a reliable solution.

Upvotes: 0

Yaron
Yaron

Reputation: 10450

Update: It seems like your code was failing also due to the use of "count" as column name. count seems to be protected keyword in DataFrame API. renaming count to "mycount" solved the problem. The below working code was modify to support spark version 1.5.2 which I used to test your issue.

df = sqlContext.read.format("com.databricks.spark.csv").option("header", "true").load("/tmp/fac_cal.csv")
df1 = df.groupBy("name", "genre").count()
df1 = df1.select(col("name"),col("genre"),col("count").alias("mycount"))
df2 = df1.groupby('name').agg(F.max("mycount").alias("max_count"))
df2 = df2.select(col('name').alias('name2'),col("max_count"))
#Now trying to join both dataframes
final_df = df1.join(df2,[df1.name == df2.name2 , df1.mycount == df2.max_count])
final_df.show()

+-----+---------+-------+-----+---------+
| name|    genre|mycount|name2|max_count|
+-----+---------+-------+-----+---------+
|brata|   comedy|      2|brata|        2|
|brata|    drama|      2|brata|        2|
|panda|adventure|      1|panda|        1|
|panda|  romance|      1|panda|        1|
|satya|   action|      3|satya|        3|
+-----+---------+-------+-----+---------+

The example for complex condition in https://spark.apache.org/docs/2.0.0/api/python/pyspark.sql.html

cond = [df.name == df3.name, df.age == df3.age]
>>> df.join(df3, cond, 'outer').select(df.name, df3.age).collect()
[Row(name=u'Alice', age=2), Row(name=u'Bob', age=5)]

can you try: 

final_df = df1.join(df2, [df1.name == df2.name , df1.mycount == df2.max_count])

Note also, that according to the spec "left" is not part of the valid join types: how – str, default ‘inner’. One of inner, outer, left_outer, right_outer, leftsemi.

Upvotes: 2

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