[SPARK-14061][SQL] implement CreateMap

## What changes were proposed in this pull request?

As we have `CreateArray` and `CreateStruct`, we should also have `CreateMap`.  This PR adds the `CreateMap` expression, and the DataFrame API, and python API.

## How was this patch tested?

various new tests.

Author: Wenchen Fan <wenchen@databricks.com>

Closes #11879 from cloud-fan/create_map.

1 files changed, 11 insertions, 0 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/functions.scala b/sql/core/src/main/scala/org/apache/spark/sql/functions.scala
index 304d747d4f..8abb9d7e4a 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/functions.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/functions.scala
@@ -905,6 +905,17 @@ object functions {
   }
 
   /**
+   * Creates a new map column. The input columns must be grouped as key-value pairs, e.g.
+   * (key1, value1, key2, value2, ...). The key columns must all have the same data type, and can't
+   * be null. The value columns must all have the same data type.
+   *
+   * @group normal_funcs
+   * @since 2.0
+   */
+  @scala.annotation.varargs
+  def map(cols: Column*): Column = withExpr { CreateMap(cols.map(_.expr)) }
+
+  /**
    * Marks a DataFrame as small enough for use in broadcast joins.
    *
    * The following example marks the right DataFrame for broadcast hash join using `joinKey`.