Joining Apache Spark data frames, with many conditional substitutions

Question

I am joining two data frame in spark using scala . My code looks very ugly because of the multiple when condition .

Can somebody please help me simplify my code?

Here is my existing code .

val columnsNameArray=schema.fieldNames

All columns name are from the array columnsNameArray and in same sequence except

val dfMainOutput = df1resultFinal.join(latestForEachKey, Seq(columnsNameArray(0), columnsNameArray(1)), "outer")
      .select($columnsNameArray(0), $columnsNameArray(1),
        when($"DataPartition_1".isNotNull, $"DataPartition_1").otherwise($"DataPartition").as("DataPartition"),

        when($"StatementTypeCode_1".isNotNull, $"StatementTypeCode_1").otherwise($"StatementTypeCode").as("StatementTypeCode"),
        when($"LineItemName_1".isNotNull, $"LineItemName_1").otherwise($"LineItemName").as("LineItemName"),
        when($"LocalLanguageLabel_1".isNotNull, $"LocalLanguageLabel_1").otherwise($"LocalLanguageLabel").as("LocalLanguageLabel"),
        when($"FinancialConceptLocal_1".isNotNull, $"FinancialConceptLocal_1").otherwise($"FinancialConceptLocal").as("FinancialConceptLocal"),
        when($"FinancialConceptGlobal_1".isNotNull, $"FinancialConceptGlobal_1").otherwise($"FinancialConceptGlobal").as("FinancialConceptGlobal"),
        when($"IsDimensional_1".isNotNull, $"IsDimensional_1").otherwise($"IsDimensional").as("IsDimensional"),
        when($"InstrumentId_1".isNotNull, $"InstrumentId_1").otherwise($"InstrumentId").as("InstrumentId"),
        when($"LineItemSequence_1".isNotNull, $"LineItemSequence_1").otherwise($"LineItemSequence").as("LineItemSequence"),
        when($"PhysicalMeasureId_1".isNotNull, $"PhysicalMeasureId_1").otherwise($"PhysicalMeasureId").as("PhysicalMeasureId"),
        when($"FinancialConceptCodeGlobalSecondary_1".isNotNull, $"FinancialConceptCodeGlobalSecondary_1").otherwise($"FinancialConceptCodeGlobalSecondary").as("FinancialConceptCodeGlobalSecondary"),
        when($"IsRangeAllowed_1".isNotNull, $"IsRangeAllowed_1").otherwise($"IsRangeAllowed").as("IsRangeAllowed"),
        when($"IsSegmentedByOrigin_1".isNotNull, $"IsSegmentedByOrigin_1").otherwise($"IsSegmentedByOrigin".cast(DataTypes.StringType)).as("IsSegmentedByOrigin"),
        when($"SegmentGroupDescription_1".isNotNull, $"SegmentGroupDescription_1").otherwise($"SegmentGroupDescription").as("SegmentGroupDescription"),
        when($"SegmentChildDescription_1".isNotNull, $"SegmentChildDescription_1").otherwise($"SegmentChildDescription").as("SegmentChildDescription"),
        when($"SegmentChildLocalLanguageLabel_1".isNotNull, $"SegmentChildLocalLanguageLabel_1").otherwise($"SegmentChildLocalLanguageLabel").as("SegmentChildLocalLanguageLabel"),
        when($"LocalLanguageLabel_languageId_1".isNotNull, $"LocalLanguageLabel_languageId_1").otherwise($"LocalLanguageLabel_languageId").as("LocalLanguageLabel_languageId"),
        when($"LineItemName_languageId_1".isNotNull, $"LineItemName_languageId_1").otherwise($"LineItemName_languageId").as("LineItemName_languageId"),
        when($"SegmentChildDescription_languageId_1".isNotNull, $"SegmentChildDescription_languageId_1").otherwise($"SegmentChildDescription_languageId").as("SegmentChildDescription_languageId"),
        when($"SegmentChildLocalLanguageLabel_languageId_1".isNotNull, $"SegmentChildLocalLanguageLabel_languageId_1").otherwise($"SegmentChildLocalLanguageLabel_languageId").as("SegmentChildLocalLanguageLabel_languageId"),
        when($"SegmentGroupDescription_languageId_1".isNotNull, $"SegmentGroupDescription_languageId_1").otherwise($"SegmentGroupDescription_languageId").as("SegmentGroupDescription_languageId"),
        when($"SegmentMultipleFundbDescription_1".isNotNull, $"SegmentMultipleFundbDescription_1").otherwise($"SegmentMultipleFundbDescription").as("SegmentMultipleFundbDescription"),
        when($"SegmentMultipleFundbDescription_languageId_1".isNotNull, $"SegmentMultipleFundbDescription_languageId_1").otherwise($"SegmentMultipleFundbDescription_languageId").as("SegmentMultipleFundbDescription_languageId"),
        when($"IsCredit_1".isNotNull, $"IsCredit_1").otherwise($"IsCredit").as("IsCredit"),
        when($"FinancialConceptLocalId_1".isNotNull, $"FinancialConceptLocalId_1").otherwise($"FinancialConceptLocalId").as("FinancialConceptLocalId"),
        when($"FinancialConceptGlobalId_1".isNotNull, $"FinancialConceptGlobalId_1").otherwise($"FinancialConceptGlobalId").as("FinancialConceptGlobalId"),
        when($"FinancialConceptCodeGlobalSecondaryId_1".isNotNull, $"FinancialConceptCodeGlobalSecondaryId_1").otherwise($"FinancialConceptCodeGlobalSecondaryId").as("FinancialConceptCodeGlobalSecondaryId"),
        when($"FFAction_1".isNotNull, $"FFAction_1").otherwise($"FFAction|!|").as("FFAction|!|"))
        .filter(!$"FFAction|!|".contains("D|!|"))

Here is the details about Header and columnsNameArry for Data frame

LineItem.organizationId|^|LineItem.lineItemId|^|StatementTypeCode|^|LineItemName|^|LocalLanguageLabel|^|FinancialConceptLocal|^|FinancialConceptGlobal|^|IsDimensional|^|InstrumentId|^|LineItemSequence|^|PhysicalMeasureId|^|FinancialConceptCodeGlobalSecondary|^|IsRangeAllowed|^|IsSegmentedByOrigin|^|SegmentGroupDescription|^|SegmentChildDescription|^|SegmentChildLocalLanguageLabel|^|LocalLanguageLabel.languageId|^|LineItemName.languageId|^|SegmentChildDescription.languageId|^|SegmentChildLocalLanguageLabel.languageId|^|SegmentGroupDescription.languageId|^|SegmentMultipleFundbDescription|^|SegmentMultipleFundbDescription.languageId|^|IsCredit|^|FinancialConceptLocalId|^|FinancialConceptGlobalId|^|FinancialConceptCodeGlobalSecondaryId|^|FFAction|!|
4295879842|^|1246|^|CUS|^|Net Sales-Customer Segment|^|相手先別の販売高（相手先別）|^|JCSNTS|^|REXM|^|False|^||^||^||^||^|False|^|False|^|CUS_JCSNTS|^||^||^|505126|^|505074|^|505074|^|505126|^|505126|^||^|505074|^|True|^|3020155|^|3015249|^||^|I|!|

Answer 1

Indeed, the sequence of when statements is very repetitive and can be refactored.

All whens are similar, except the last one, so we can create a shortcut function that takes the column name without the _1 suffix and returns the resulting Column:

private def whenExpr(colName: String): Column = {
  val columnSuffix1 = col(colName + "_1")
  val originalColumn = col(colName)
  when(columnSuffix1.isNotNull, columnSuffix1).otherwise(originalColumn).as(colName)
}

Then, we can put all the base column names in a sequence and transform them into columns using this def:

private val columnSelectionsWithWhen = Seq(
  "DataPartition",
  "StatementTypeCode",
  "LineItemName"
// ... other column names
).map(whenExpr)

Now we can obtain the full sequence of columns that is to pass into .select call:

val selectedColumns =
  Seq(col(columnsNameArray(0)), col(columnsNameArray(1))) ++
    columnSelectionsWithWhen :+
    when($"FFAction_1".isNotNull, $"FFAction_1").otherwise($"FFAction|!|").as("FFAction|!|")

The original call may now be reduced to the following:

val dfMainOutput = df1resultFinal.join(latestForEachKey,
                                       Seq(columnsNameArray(0), columnsNameArray(1)),
                                       "outer")
  .select(selectedColumns:_*)
  .filter(!$"FFAction|!|".contains("D|!|"))