Adding DataFrame.Dtypes support (#635)

Author: Niharikadutta

src/csharp/Microsoft.Spark.E2ETest/IpcTests/Sql/DataFrameTests.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using Apache.Arrow;
 using Microsoft.Data.Analysis;
@@ -459,6 +460,13 @@ public void TestSignaturesV2_3_X()
 
             Assert.Equal(2, _df.Columns().ToArray().Length);
 
+            var expected = new List<Tuple<string, string>>
+            {
+                new Tuple<string, string>("age", "integer"),
+                new Tuple<string, string>("name", "string")
+            };
+            Assert.Equal(expected, _df.DTypes());
+
             Assert.IsType<bool>(_df.IsLocal());
 
             Assert.IsType<bool>(_df.IsStreaming());

src/csharp/Microsoft.Spark/Sql/DataFrame.cs

@@ -84,6 +84,14 @@ public void Explain(bool extended = false)
             Console.WriteLine((string)execution.Invoke(extended ? "toString" : "simpleString"));
         }
 
+        /// <summary>
+        /// Returns all column names and their data types as an IEnumerable of Tuples.
+        /// </summary>
+        /// <returns>IEnumerable of Tuple of strings</returns>
+        public IEnumerable<Tuple<string, string>> DTypes() =>
+            Schema().Fields.Select(
+                f => new Tuple<string, string>(f.Name, f.DataType.SimpleString));
+
         /// <summary>
         /// Returns all column names.
         /// </summary>