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her_sampler.py
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her_sampler.py
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import numpy as np
def make_sample_her_transitions(replay_strategy, replay_k, reward_fun):
"""Creates a sample function that can be used for HER experience replay.
Args:
replay_strategy (in ['future', 'none']): the HER replay strategy; if set to 'none',
regular DDPG experience replay is used
replay_k (int): the ratio between HER replays and regular replays (e.g. k = 4 -> 4 times
as many HER replays as regular replays are used)
reward_fun (function): function to re-compute the reward with substituted goals
"""
if replay_strategy == 'future':
future_p = 1 - (1. / (1 + replay_k))
else: # 'replay_strategy' == 'none'
future_p = 0
def _sample_her_transitions(episode_batch, batch_size_in_transitions):
"""episode_batch is {key: array(buffer_size x T x dim_key)}
"""
T = episode_batch['u'].shape[1]
rollout_batch_size = episode_batch['u'].shape[0]
batch_size = batch_size_in_transitions
# Select which episodes and time steps to use.
episode_idxs = np.random.randint(0, rollout_batch_size, batch_size)
t_samples = np.random.randint(T, size=batch_size)
transitions = {key: episode_batch[key][episode_idxs, t_samples].copy()
for key in episode_batch.keys()}
# Select future time indexes proportional with probability future_p. These
# will be used for HER replay by substituting in future goals.
her_indexes = np.where(np.random.uniform(size=batch_size) < future_p)
future_offset = np.random.uniform(size=batch_size) * (T - t_samples)
future_offset = future_offset.astype(int)
future_t = (t_samples + 1 + future_offset)[her_indexes]
# Replace goal with achieved goal but only for the previously-selected
# HER transitions (as defined by her_indexes). For the other transitions,
# keep the original goal.
future_ag = episode_batch['ag'][episode_idxs[her_indexes], future_t]
transitions['g'][her_indexes] = future_ag
# Reconstruct info dictionary for reward computation.
info = {}
for key, value in transitions.items():
if key.startswith('info_'):
info[key.replace('info_', '')] = value
# Re-compute reward since we may have substituted the goal.
reward_params = {k: transitions[k] for k in ['ag_2', 'g']}
reward_params['info'] = info
transitions['r'] = reward_fun(**reward_params)
transitions = {k: transitions[k].reshape(batch_size, *transitions[k].shape[1:])
for k in transitions.keys()}
assert(transitions['u'].shape[0] == batch_size_in_transitions)
return transitions
return _sample_her_transitions