pyspark - Spark: Merge 2 dataframes by adding row index/number on both dataframes

Question

Q: Is there is any way to merge two dataframes or copy a column of a dataframe to another in PySpark?

For example, I have two Dataframes:

DF1              
C1                    C2                                                        
23397414             20875.7353   
5213970              20497.5582   
41323308             20935.7956   
123276113            18884.0477   
76456078             18389.9269 

the seconde dataframe

DF2
C3                       C4
2008-02-04               262.00                 
2008-02-05               257.25                 
2008-02-06               262.75                 
2008-02-07               237.00                 
2008-02-08               231.00 

Then i want to add C3 of DF2 to DF1 like this:

New DF              
    C1                    C2          C3                                              
    23397414             20875.7353   2008-02-04
    5213970              20497.5582   2008-02-05
    41323308             20935.7956   2008-02-06
    123276113            18884.0477   2008-02-07
    76456078             18389.9269   2008-02-08

I hope this example was clear.

Answer 1

rownum + window function i.e solution 1 or zipWithIndex.map i.e solution 2 should help in this case.

Solution 1 : You can use window functions to get this kind of

Then I would suggest you to add rownumber as additional column name to Dataframe say df1.

  DF1              
    C1                    C2                 columnindex                                             
    23397414             20875.7353            1
    5213970              20497.5582            2
    41323308             20935.7956            3
    123276113            18884.0477            4
    76456078             18389.9269            5

the second dataframe

DF2
C3                       C4             columnindex
2008-02-04               262.00            1        
2008-02-05               257.25            2      
2008-02-06               262.75            3      
2008-02-07               237.00            4          
2008-02-08               231.00            5

Now .. do inner join of df1 and df2 that's all... you will get below ouput

something like this

from pyspark.sql.window import Window
from pyspark.sql.functions import rowNumber

w = Window().orderBy()

df1 = ....  // as showed above df1

df2 = ....  // as shown above df2


df11 =  df1.withColumn("columnindex", rowNumber().over(w))
  df22 =  df2.withColumn("columnindex", rowNumber().over(w))

newDF = df11.join(df22, df11.columnindex == df22.columnindex, 'inner').drop(df22.columnindex)
newDF.show()



New DF              
    C1                    C2          C3                                              
    23397414             20875.7353   2008-02-04
    5213970              20497.5582   2008-02-05
    41323308             20935.7956   2008-02-06
    123276113            18884.0477   2008-02-07
    76456078             18389.9269   2008-02-08

Solution 2 : Another good way(probably this is best :)) in scala, which you can translate to pyspark :

/**
* Add Column Index to dataframe 
*/
def addColumnIndex(df: DataFrame) = sqlContext.createDataFrame(
  // Add Column index
  df.rdd.zipWithIndex.map{case (row, columnindex) => Row.fromSeq(row.toSeq :+ columnindex)},
  // Create schema
  StructType(df.schema.fields :+ StructField("columnindex", LongType, false))
)

// Add index now...
val df1WithIndex = addColumnIndex(df1)
val df2WithIndex = addColumnIndex(df2)

 // Now time to join ...
val newone = df1WithIndex
  .join(df2WithIndex , Seq("columnindex"))
  .drop("columnindex")