!10044 fix get num classes of concat

From: @luoyang42
Reviewed-by: @liucunwei,@heleiwang,@liucunwei
Signed-off-by: @liucunwei,@liucunwei

mindspore/ccsrc/minddata/dataset/engine/datasetops/concat_op.cc

@@ -196,5 +196,20 @@ Status ConcatOp::PreAccept(NodePass *p, bool *modified) {
   return p->PreRunOnNode(shared_from_base<ConcatOp>(), modified);
 }
 
+// Gets the number of classes
+Status ConcatOp::GetNumClasses(int64_t *num_classes) {
+  int64_t max_num_classes = -1;
+  for (const auto &child : child_) {
+    // Choose a dataset which can get valid num_classes
+    int64_t tmp_num_classes = -1;
+    child->GetNumClasses(&tmp_num_classes);
+    if (tmp_num_classes > max_num_classes) {
+      max_num_classes = tmp_num_classes;
+    }
+  }
+  *num_classes = max_num_classes;
+  return Status::OK();
+}
+
 }  // namespace dataset
 }  // namespace mindspore

mindspore/ccsrc/minddata/dataset/engine/datasetops/concat_op.h

@@ -111,6 +111,11 @@ class ConcatOp : public PipelineOp {
   /// \return Status of the node visit
   Status PreAccept(NodePass *p, bool *modified) override;
 
+  /// \brief Gets the number of classes
+  /// \param[out] num_classes the number of classes
+  /// \return Status - The status code return
+  Status GetNumClasses(int64_t *num_classes) override;
+
  private:
   Status Verify(int32_t id, const std::unique_ptr<DataBuffer> &buf);
 

tests/ut/python/dataset/test_datasets_manifestop.py

@@ -113,6 +113,20 @@ def test_manifest_dataset_multi_label_onehot():
         count = count + 1
 
 
+def test_manifest_dataset_get_num_class():
+    data = ds.ManifestDataset(DATA_FILE, decode=True, shuffle=False)
+    assert data.num_classes() == 3
+
+    padded_samples = [{'image': np.zeros(1, np.uint8), 'label': np.array(1, np.int32)}]
+    padded_ds = ds.PaddedDataset(padded_samples)
+
+    data = data.repeat(2)
+    padded_ds = padded_ds.repeat(2)
+
+    data1 = data + padded_ds
+    assert data1.num_classes() == 3
+
+
 if __name__ == '__main__':
     test_manifest_dataset_train()
     test_manifest_dataset_eval()
@@ -120,3 +134,4 @@ if __name__ == '__main__':
     test_manifest_dataset_get_class_index()
     test_manifest_dataset_multi_label()
     test_manifest_dataset_multi_label_onehot()
+    test_manifest_dataset_get_num_class()