tf.layers.flatten: Added support for None dimension

src/TensorFlowNET.Core/APIs/tf.layers.cs

@@ -15,6 +15,8 @@
 ******************************************************************************/
 
 using System.Collections.Generic;
+using System.Linq;
+using NumSharp;
 using Tensorflow.Keras.Layers;
 using Tensorflow.Operations.Activation;
 using static Tensorflow.Binding;
@@ -182,6 +184,7 @@ namespace Tensorflow
                 string name = null,
                 string data_format = "channels_last")
             {
+                var input_shape = inputs.shape;
                 if (inputs.shape.Length == 0)
                     throw new ValueError($"Input 0 of layer flatten is incompatible with the layer: : expected min_ndim={1}, found ndim={0}. Full shape received: ()");
 
@@ -193,9 +196,25 @@ namespace Tensorflow
                     inputs = array_ops.transpose(inputs, premutation.ToArray());
                 }
 
-                var ret = array_ops.reshape(inputs, new int[] {inputs.shape[0], -1});
-                ret.set_shape(new int[] {inputs.shape[0], -1});
+                var ret = array_ops.reshape(inputs, new int[] {input_shape[0], -1});
+                ret.shape = ret.shape;
+                //ret.set_shape(compute_output_shape(ret.shape));
                 return ret;
+
+                int[] compute_output_shape(int[] inputshape)
+                {
+                    if (inputshape == null || inputshape.Length == 0)
+                        inputshape = new int[] {1};
+
+                    if (inputshape.Skip(1).All(d => d > 0))
+                    {
+                        int[] output_shape = new int[2];
+                        output_shape[0] = inputshape[0];
+                        output_shape[1] = inputshape.Skip(1).Aggregate(1, (acc, rhs) => acc*rhs); //calculate size of all the rest dimensions
+                        return output_shape;
+                    } else
+                        return new int[] {inputshape[0], -1}; //-1 == Binding.None
+                }
             }
         }
     }

test/TensorFlowNET.UnitTest/layers_test/flatten.cs

@@ -36,5 +36,14 @@ namespace TensorFlowNET.UnitTest.layers_test
             var input = tf.placeholder(TF_DataType.TF_INT32, new TensorShape());
             new Action(() => sess.run(tf.layers.flatten(input), (input, NDArray.Scalar(6)))).Should().Throw<ValueError>();
         }
+
+        [TestMethod]
+        public void Case4()
+        {
+            var sess = tf.Session().as_default();
+
+            var input = tf.placeholder(TF_DataType.TF_INT32, new TensorShape(3, 4, None, 1, 2));
+            sess.run(tf.layers.flatten(input), (input, np.arange(3 * 4 * 3 * 1 * 2).reshape(3, 4, 3, 1, 2))).Should().BeShaped(3, 24);
+        }
     }
 }