Add a columnToList method as that's commonly needed

src/main/scala/com/github/mrpowers/spark/daria/sql/DataFrameHelpers.scala

@@ -92,6 +92,41 @@ object DataFrameHelpers extends DataFrameValidator {
     df.select(colName).collect().map(r => r(0).asInstanceOf[T])
   }
 
+  /**
+   * Converts a DataFrame column to a List of values
+   * '''N.B. This method uses `collect` and should only be called on small DataFrames.'''
+   *
+   * This function converts a column to a list of items.
+   *
+   * Suppose we have the following `sourceDF`:
+   *
+   * {{{
+   * +---+
+   * |num|
+   * +---+
+   * |  1|
+   * |  2|
+   * |  3|
+   * +---+
+   * }}}
+   *
+   * Let's convert the `num` column to a List of values.  Let's run the code and view the results.
+   *
+   * {{{
+   * val actual = DataFrameHelpers.columnToList[Int](sourceDF, "num")
+   *
+   * println(actual)
+   *
+   * // List(1, 2, 3)
+   * }}}
+   */
+  def columnToList[T: ClassTag](
+    df: DataFrame,
+    colName: String
+  ): List[T] = {
+    columnToArray[T](df, colName).toList
+  }
+
   /**
    * Converts a DataFrame to an Array of Maps
    * '''N.B. This method uses `collect` and should only be called on small DataFrames.'''

src/test/scala/com/github/mrpowers/spark/daria/sql/DataFrameHelpersTest.scala

@@ -65,6 +65,28 @@ object DataFrameHelpersTest
 
     }
 
+    'columnToList - {
+
+      "converts a column to a list" - {
+
+        val sourceDF = spark.createDF(
+          List(
+            1,
+            2,
+            3
+          ), List(
+            ("num", IntegerType, true)
+          )
+        )
+
+        val actual = DataFrameHelpers.columnToList[Int](sourceDF, "num")
+
+        actual ==> List(1, 2, 3)
+
+      }
+
+    }
+
     'toArrayOfMaps - {
 
       "converts a DataFrame into an array of maps" - {