how to select all columns that starts with a common label

Question

I have a dataframe in Spark 1.6 and want to select just some columns out of it. The column names are like:

colA, colB, colC, colD, colE, colF-0, colF-1, colF-2
<         


        

Answer 1

I wrote a function that does that. Read the comments to see how it works.

  /**
    * Given a sequence of prefixes, select suitable columns from [[DataFrame]]
    * @param columnPrefixes Sequence of prefixes
    * @param dF Incoming [[DataFrame]]
    * @return [[DataFrame]] with prefixed columns selected
    */
  def selectPrefixedColumns(columnPrefixes: Seq[String], dF: DataFrame): DataFrame = {
    // Find out if given column name matches any of the provided prefixes
    def colNameStartsWith: String => Boolean = (colName: String) =>
        columnsPrefix.map(prefix => colName.startsWith(prefix)).reduce(_ || _)
    // Filter columns list by checking against given prefixes sequence
    val columns = dF.columns.filter(colNameStartsWith)
    // Select filtered columns list
    dF.select(columns.head, columns.tail:_*)
  }