python – How to remove all data from TFRecordDataset except the first record

The following code created a TFRecordDataset from test_filenamesand it contains 10000 records:

test_dataset = tf.data.TFRecordDataset([test_filenames])

I want to keep the first record in the test_dataset and remove all other records for testing.

Here is the dummy code:

test_dataset = test_dataset.removeAllExceptFirst()

...

first_record = test_dataset.getItem(0)

test_dataset = test_dataset.removeAll()
test_dataset = test_dataset.add(first_record)

Is there any existing method for implementing this feature?

Here is the test for using “test_dataset.batch(1).take(1)“, it does not work as expected:

def test_function(record):
    keys_to_features = {
        "test1": tf.io.FixedLenFeature((), tf.string, default_value=""),
        'test2': tf.io.FixedLenFeature([], tf.string),
        "test3": tf.io.FixedLenFeature((), tf.string)
    }

    features = tf.io.parse_single_example(record, keys_to_features)
    
    print("features: {}".format(features))

    return None, None

test_dataset = tf.data.TFRecordDataset([test_filenames])
test_dataset = test_dataset.batch(1).take(1)
test_dataset = test_dataset.map(test_function)

Here is the error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/tmp/ipykernel_11776/3885954589.py in <cell line: 3>()
      1 test_dataset = tf.data.TFRecordDataset([test_filenames])
      2 test_dataset = test_dataset.batch(1).take(1)
----> 3 test_dataset = test_dataset.map(test_function)

/usr/local/lib/python3.8/site-packages/tensorflow/python/data/ops/dataset_ops.py in map(self, map_func, num_parallel_calls, deterministic, name)
   2014         warnings.warn("The `deterministic` argument has no effect unless the "
   2015                       "`num_parallel_calls` argument is specified.")
-> 2016       return MapDataset(self, map_func, preserve_cardinality=True, name=name)
   2017     else:
   2018       return ParallelMapDataset(

/usr/local/lib/python3.8/site-packages/tensorflow/python/data/ops/dataset_ops.py in __init__(self, input_dataset, map_func, use_inter_op_parallelism, preserve_cardinality, use_legacy_function, name)
   5189     self._use_inter_op_parallelism = use_inter_op_parallelism
   5190     self._preserve_cardinality = preserve_cardinality
-> 5191     self._map_func = structured_function.StructuredFunctionWrapper(
   5192         map_func,
   5193         self._transformation_name(),

/usr/local/lib/python3.8/site-packages/tensorflow/python/data/ops/structured_function.py in __init__(self, func, transformation_name, dataset, input_classes, input_shapes, input_types, input_structure, add_to_graph, use_legacy_function, defun_kwargs)
    269         fn_factory = trace_tf_function(defun_kwargs)
    270 
--> 271     self._function = fn_factory()
    272     # There is no graph to add in eager mode.
    273     add_to_graph &= not context.executing_eagerly()

/usr/local/lib/python3.8/site-packages/tensorflow/python/eager/function.py in get_concrete_function(self, *args, **kwargs)
   3068          or `tf.Tensor` or `tf.TensorSpec`.
   3069     """
-> 3070     graph_function = self._get_concrete_function_garbage_collected(
   3071         *args, **kwargs)
   3072     graph_function._garbage_collector.release()  # pylint: disable=protected-access

/usr/local/lib/python3.8/site-packages/tensorflow/python/eager/function.py in _get_concrete_function_garbage_collected(self, *args, **kwargs)
   3034       args, kwargs = None, None
   3035     with self._lock:
-> 3036       graph_function, _ = self._maybe_define_function(args, kwargs)
   3037       seen_names = set()
   3038       captured = object_identity.ObjectIdentitySet(

/usr/local/lib/python3.8/site-packages/tensorflow/python/eager/function.py in _maybe_define_function(self, args, kwargs)
   3290 
   3291           self._function_cache.add_call_context(cache_key.call_context)
-> 3292           graph_function = self._create_graph_function(args, kwargs)
   3293           self._function_cache.add(cache_key, cache_key_deletion_observer,
   3294                                    graph_function)

/usr/local/lib/python3.8/site-packages/tensorflow/python/eager/function.py in _create_graph_function(self, args, kwargs, override_flat_arg_shapes)
   3128     arg_names = base_arg_names + missing_arg_names
   3129     graph_function = ConcreteFunction(
-> 3130         func_graph_module.func_graph_from_py_func(
   3131             self._name,
   3132             self._python_function,

/usr/local/lib/python3.8/site-packages/tensorflow/python/framework/func_graph.py in func_graph_from_py_func(name, python_func, args, kwargs, signature, func_graph, autograph, autograph_options, add_control_dependencies, arg_names, op_return_value, collections, capture_by_value, override_flat_arg_shapes, acd_record_initial_resource_uses)
   1159         _, original_func = tf_decorator.unwrap(python_func)
   1160 
-> 1161       func_outputs = python_func(*func_args, **func_kwargs)
   1162 
   1163       # invariant: `func_outputs` contains only Tensors, CompositeTensors,

/usr/local/lib/python3.8/site-packages/tensorflow/python/data/ops/structured_function.py in wrapped_fn(*args)
    246           attributes=defun_kwargs)
    247       def wrapped_fn(*args):  # pylint: disable=missing-docstring
--> 248         ret = wrapper_helper(*args)
    249         ret = structure.to_tensor_list(self._output_structure, ret)
    250         return [ops.convert_to_tensor

/usr/local/lib/python3.8/site-packages/tensorflow/python/data/ops/structured_function.py in wrapper_helper(*args)
    175       if not _should_unpack(nested_args):
    176         nested_args = (nested_args,)
--> 177       ret = autograph.tf_convert(self._func, ag_ctx)(*nested_args)
    178       if _should_pack(ret):
    179         ret = tuple(ret)

/usr/local/lib/python3.8/site-packages/tensorflow/python/autograph/impl/api.py in wrapper(*args, **kwargs)
    690       except Exception as e:  # pylint:disable=broad-except
    691         if hasattr(e, 'ag_error_metadata'):
--> 692           raise e.ag_error_metadata.to_exception(e)
    693         else:
    694           raise

ValueError: in user code:

    File "/tmp/ipykernel_11776/3804092897.py", line 8, in test_function  *
        features = tf.io.parse_single_example(record, keys_to_features)

    ValueError: Input serialized must be a scalar

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