Spark scala modify DataFrame columns based on other DataFrame

Question

I am new to spark and scala and would like to know how to perform operations between 2 dataframes. In my case I have these two dataframes:

DF1:

ID_EMPLOYEE sup_id_1    desc_1  sup_id_2    desc_2  ...     sup_id_18   desc_18 sup_id_19   desc_19
AAAAAAAA    SUP_ID1             SUP_ID2             ...     SUP_ID3             SUP_ID4 
BBBBBBBBB   SUP_ID4             SUP_ID6             ...     SUP_ID6             SUP_ID6 
CCCCCCCCC   SUP_ID5             SUP_ID5             ...     SUP_ID5             SUP_ID5 
DDDDDDDD    SUP_ID7             SUP_ID7             ...     SUP_ID7             SUP_ID7

and

DF2:

Key     Desc
SUP_ID1 Desc1
SUP_ID2 Desc2
SUP_ID3 Desc3
SUP_ID4 Desc4
SUP_ID5 Desc5
SUP_ID6 Desc6
SUP_ID7 Desc7

I would like to modify from DF1 the desc_* columns based on DF2, because in DF1 they are empty. The way to fill it would be looking at the sup_id_* columns of DF1 and the Key column of DF2, adding in the desc_* column of DF1 the value of the Desc column of DF2.

I don't know what would be the easiest way to do it, since with my knowledge I can only think of treating the DataFrames as SQL tables and make as many joins as I have desc_* columns, but that is not the most efficient way.

If you say not the mots efficient way, then obviously you have some insight you are not sharing. — Ged
– Ged, Commented Dec 15, 2020 at 12:11

mvasyliv · Accepted Answer · 2020-12-16 13:55:01Z

  import spark.implicits._

  import org.apache.spark.sql.functions.{col}

  case class Source1(
                      idEmploye: String,
                      sup_id_1: String,
                      desc_1: Option[String],
                      sup_id_2: String,
                      desc_2: Option[String],
                      sup_id_3: String,
                      desc_3: Option[String],
                      sup_id_4: String,
                      desc_4: Option[String],
                      sup_id_5: String,
                      desc_5: Option[String],
                      sup_id_6: String,
                      desc_6: Option[String]
                    )

  val source1 = Seq(
    Source1("AAAAAAAA", "SUP_ID1", None, "SUP_ID2", None, "SUP_ID3", None, "SUP_ID4", None, "SUP_ID5", None, "SUP_ID8", None),
    Source1("BBBBBBBBB", "SUP_ID4", None, "SUP_ID6", None, "SUP_ID6", None, "SUP_ID6", None, "SUP_ID6", None, "SUP_ID8", None),
    Source1("CCCCCCCCC", "SUP_ID5", None, "SUP_ID5", None, "SUP_ID5", None, "SUP_ID5", None, "SUP_ID5", None, "SUP_ID8", None),
    Source1("DDDDDDDD", "SUP_ID7", None, "SUP_ID7", None, "SUP_ID7", None, "SUP_ID7", None, "SUP_ID7", None, "SUP_ID8", None)
  ).toDF()

  val source2 = Seq(
    ("SUP_ID1", "Desc1"),
    ("SUP_ID2", "Desc2"),
    ("SUP_ID3", "Desc3"),
    ("SUP_ID4", "Desc4"),
    ("SUP_ID5", "Desc5"),
    ("SUP_ID6", "Desc6"),
    ("SUP_ID7", "Desc7")
  ).toDF("Key", "Desc")

  val listColumns = 1 to ((source1.columns.length - 1) / 2) by 1

  val source12 = listColumns.foldLeft(source1){(memoDF, colName) =>
    val df1 = memoDF.join(source2,
      memoDF.col(s"sup_id_$colName") === source2.col("key"),
    "left_outer")

    df1.drop("key", s"desc_${colName}")
      .withColumnRenamed("Desc", s"desc_$colName")
  }

    val resDF = source12.select(source1.columns.map(name => col(name)):_*)

  resDF.printSchema
//  root
//  |-- idEmploye: string (nullable = true)
//  |-- sup_id_1: string (nullable = true)
//  |-- desc_1: string (nullable = true)
//  |-- sup_id_2: string (nullable = true)
//  |-- desc_2: string (nullable = true)
//  |-- sup_id_3: string (nullable = true)
//  |-- desc_3: string (nullable = true)
//  |-- sup_id_4: string (nullable = true)
//  |-- desc_4: string (nullable = true)
//  |-- sup_id_5: string (nullable = true)
//  |-- desc_5: string (nullable = true)
//  |-- sup_id_6: string (nullable = true)
//  |-- desc_6: string (nullable = true)

  resDF.show(false)
//  +---------+--------+------+--------+------+--------+------+--------+------+--------+------+--------+------+
//  |idEmploye|sup_id_1|desc_1|sup_id_2|desc_2|sup_id_3|desc_3|sup_id_4|desc_4|sup_id_5|desc_5|sup_id_6|desc_6|
//  +---------+--------+------+--------+------+--------+------+--------+------+--------+------+--------+------+
//  |AAAAAAAA |SUP_ID1 |Desc1 |SUP_ID2 |Desc2 |SUP_ID3 |Desc3 |SUP_ID4 |Desc4 |SUP_ID5 |Desc5 |SUP_ID8 |null  |
//  |BBBBBBBBB|SUP_ID4 |Desc4 |SUP_ID6 |Desc6 |SUP_ID6 |Desc6 |SUP_ID6 |Desc6 |SUP_ID6 |Desc6 |SUP_ID8 |null  |
//  |CCCCCCCCC|SUP_ID5 |Desc5 |SUP_ID5 |Desc5 |SUP_ID5 |Desc5 |SUP_ID5 |Desc5 |SUP_ID5 |Desc5 |SUP_ID8 |null  |
//  |DDDDDDDD |SUP_ID7 |Desc7 |SUP_ID7 |Desc7 |SUP_ID7 |Desc7 |SUP_ID7 |Desc7 |SUP_ID7 |Desc7 |SUP_ID8 |null  |
//  +---------+--------+------+--------+------+--------+------+--------+------+--------+------+--------+------+

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