Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/6072#discussion_r30115116
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/Column.scala ---
@@ -309,6 +309,62 @@ class Column(protected[sql] val expr: Expression)
extends Logging {
def eqNullSafe(other: Any): Column = this <=> other
/**
+ * Evaluates a list of conditions and returns one of multiple possible
result expressions.
+ * If otherwise is not defined at the end, null is returned for
unmatched conditions.
+ *
+ * {{{
+ * // Example: encoding gender string column into integer.
+ *
+ * // Scala:
+ * people.select(when(people("gender") === "male", 0)
+ * .when(people("gender") === "female", 1)
+ * .otherwise(2))
+ *
+ * // Java:
+ * people.select(when(col("gender").equalTo("male"), 0)
+ * .when(col("gender").equalTo("female"), 1)
+ * .otherwise(2))
+ * }}}
+ *
+ * @group expr_ops
+ */
+ def when(condition: Column, value: Any):Column = this.expr match {
+ case CaseWhen(branches: Seq[Expression]) =>
+ CaseWhen(branches ++ Seq(lit(condition).expr, lit(value).expr))
+ case _ =>
+ throw new IllegalArgumentException(
+ "when() can only be applied on a Column previously generated by
when() function")
+ }
+
+ /**
+ * Evaluates a list of conditions and returns one of multiple possible
result expressions.
+ * If otherwise is not defined at the end, null is returned for
unmatched conditions.
+ *
+ * {{{
+ * // Example: encoding gender string column into integer.
+ *
+ * // Scala:
+ * people.select(when(people("gender") === "male", 0)
+ * .when(people("gender") === "female", 1)
+ * .otherwise(2))
+ *
+ * // Java:
+ * people.select(when(col("gender").equalTo("male"), 0)
+ * .when(col("gender").equalTo("female"), 1)
+ * .otherwise(2))
+ * }}}
+ *
+ * @group expr_ops
+ */
+ def otherwise(value: Any):Column = this.expr match {
+ case CaseWhen(branches: Seq[Expression]) =>
+ CaseWhen(branches :+ lit(value).expr)
--- End diff --
What if user mistakenly call `otherwise` twice? Then we will build a wrong
`CaseWhen` expression here. Maybe we should create a helper class like what we
did for NA functions and aggregate functions?
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