add support for floats and doubles (tensorflow#104)

Author: Ivan Gavryliuk

src/Parquet.Test/EndToEndTypeTest.cs

@@ -34,5 +34,36 @@ public void Strings(string input)
 
          Assert.Equal(ds[0].GetString(0), ds1[0].GetString(0));
       }
+
+      [Fact]
+      public void Floats()
+      {
+         var ds = new DataSet(new SchemaElement<float>("f"));
+         ds.Add((float)1.23);
+
+         var ms = new MemoryStream();
+         ParquetWriter.Write(ds, ms);
+
+         ms.Position = 0;
+         DataSet ds1 = ParquetReader.Read(ms);
+
+         Assert.Equal(ds[0].GetFloat(0), ds1[0].GetFloat(0));
+      }
+
+      [Fact]
+      public void Doubles()
+      {
+         var ds = new DataSet(new SchemaElement<double>("d"));
+         ds.Add((double)12.34);
+
+         var ms = new MemoryStream();
+         ParquetWriter.Write(ds, ms);
+
+         ms.Position = 0;
+         DataSet ds1 = ParquetReader.Read(ms);
+
+         Assert.Equal(ds[0].GetDouble(0), ds1[0].GetDouble(0));
+      }
+
    }
 }

src/Parquet/File/TypeFactory.cs

@@ -27,6 +27,8 @@ public TypeTag(Thrift.Type ptype, Thrift.ConvertedType? convertedType)
          { typeof(int), new TypeTag(Thrift.Type.INT32, null) },
          { typeof(bool), new TypeTag(Thrift.Type.BOOLEAN, null) },
          { typeof(string), new TypeTag(Thrift.Type.BYTE_ARRAY, Thrift.ConvertedType.UTF8) },
+         { typeof(float), new TypeTag(Thrift.Type.FLOAT, null) },
+         { typeof(double), new TypeTag(Thrift.Type.DOUBLE, null) },
          // is the coerced type TIMESTAMP_MILLS but holds backward-compatilibility with Impala and HIVE
          { typeof(DateTimeOffset), new TypeTag(Thrift.Type.INT96, null) }
       };
@@ -37,7 +39,7 @@ public static void AdjustSchema(Thrift.SchemaElement schema, Type systemType)
          {
             string supportedTypes = string.Join(", ", TypeToTag.Keys.Select(t => t.ToString()));
 
-            throw new NotSupportedException($"system type {systemType} is not supported, we currently support only these types: '{supportedTypes}'");
+            throw new NotSupportedException($"system type {systemType} is not supported, list of supported types: '{supportedTypes}'");
          }
 
          schema.Type = tag.PType;

src/Parquet/File/Values/PlainValuesWriter.cs

@@ -180,7 +180,7 @@ private void WriteInt96(BinaryWriter writer, SchemaElement schema, IList data)
       private static void WriteDouble(BinaryWriter writer, SchemaElement schema, IList data)
       {
          var lst = (List<double>)data;
-         foreach (float d in lst)
+         foreach (double d in lst)
          {
             writer.Write(d);
          }