Fix partial minibatch computation in GAIL dataset. (#724)

* Fix partial minibatch computation in GAIL dataset.

* Updated changelog.

* Added name to bottom of changelog.

Author: richardwu

docs/misc/changelog.rst

@@ -22,16 +22,16 @@ Breaking Changes:
 
    - Algorithms no longer import from each other, and ``common`` does not import from algorithms.
    - ``a2c/utils.py`` removed and split into other files:
-      
-      - common/tf_util.py: ``sample``, ``calc_entropy``, ``mse``, ``avg_norm``, ``total_episode_reward_logger``, 
-        ``q_explained_variance``, ``gradient_add``, ``avg_norm``, ``check_shape``, 
+
+      - common/tf_util.py: ``sample``, ``calc_entropy``, ``mse``, ``avg_norm``, ``total_episode_reward_logger``,
+        ``q_explained_variance``, ``gradient_add``, ``avg_norm``, ``check_shape``,
         ``seq_to_batch``, ``batch_to_seq``.
       - common/tf_layers.py: ``conv``, ``linear``, ``lstm``, ``_ln``, ``lnlstm``, ``conv_to_fc``, ``ortho_init``.
       - a2c/a2c.py: ``discount_with_dones``.
       - acer/acer_simple.py: ``get_by_index``, ``EpisodeStats``.
       - common/schedules.py: ``constant``, ``linear_schedule``, ``middle_drop``, ``double_linear_con``, ``double_middle_drop``,
         ``SCHEDULES``, ``Scheduler``.
-   
+
    - ``trpo_mpi/utils.py`` functions moved (``traj_segment_generator`` moved to ``common/runners.py``, ``flatten_lists`` to ``common/misc_util.py``).
    - ``ppo2/ppo2.py`` functions moved (``safe_mean`` to ``common/math_util.py``, ``constfn`` and ``get_schedule_fn`` to ``common/schedules.py``).
    - ``sac/policies.py`` function ``mlp`` moved to ``common/tf_layers.py``.
@@ -69,6 +69,7 @@ Bug Fixes:
 - Fixed a bug in ``BaseRLModel`` when seeding vectorized environments. (@NeoExtended)
 - Fixed ``num_timesteps`` computation to be consistent between algorithms (updated after ``env.step()``)
   Only ``TRPO`` and ``PPO1`` update it differently (after synchronization) because they rely on MPI
+- Fixed partial minibatch computation in ExpertDataset (@richardwu)
 
 Deprecations:
 ^^^^^^^^^^^^^
@@ -652,4 +653,4 @@ Thanks to @bjmuld @iambenzo @iandanforth @r7vme @brendenpetersen @huvar @abhiskk
 @XMaster96 @kantneel @Pastafarianist @GerardMaggiolino @PatrickWalter214 @yutingsz @sc420 @Aaahh @billtubbs
 @Miffyli @dwiel @miguelrass @qxcv @jaberkow @eavelardev @ruifeng96150 @pedrohbtp @srivatsankrishnan @evilsocket
 @MarvineGothic @jdossgollin @SyllogismRXS @rusu24edward @jbulow @Antymon @seheevic @justinkterry @edbeeching
-@flodorner @KuKuXia @NeoExtended @solliet @mmcenta
+@flodorner @KuKuXia @NeoExtended @solliet @mmcenta @richardwu

stable_baselines/gail/dataset/dataset.py

@@ -204,7 +204,7 @@ def __init__(self, indices, observations, actions, batch_size, n_workers=1,
         self.n_minibatches = len(indices) // batch_size
         # Add a partial minibatch, for instance
         # when there is not enough samples
-        if partial_minibatch and len(indices) / batch_size > 0:
+        if partial_minibatch and len(indices) % batch_size > 0:
             self.n_minibatches += 1
         self.batch_size = batch_size
         self.observations = observations