class Recommender(object):
"""
Contains attributes and methods that needed to train a sequential
recommendation model. Models are trained by many tuples of
(users, sequences, targets, negatives) and negatives are from negative
sampling: for any known tuple of (user, sequence, targets), one or more
items are randomly sampled to act as negatives.
Parameters
----------
n_iter: int,
Number of iterations to run.
batch_size: int,
Minibatch size.
l2: float,
L2 loss penalty, also known as the 'lambda' of l2 regularization.
neg_samples: int,
Number of negative samples to generate for each targets.
If targets=3 and neg_samples=3, then it will sample 9 negatives.
learning_rate: float,
Initial learning rate.
use_cuda: boolean,
Run the model on a GPU or CPU.
model_args: args,
Model-related arguments, like latent dimensions.
"""
def __init__(self,
n_iter=None,
batch_size=None,
l2=None,
neg_samples=None,
learning_rate=None,
use_cuda=False,
checkpoint=None,
model_args=None):
# model related
self._num_items = None
self._num_users = None
self._net = None
self.model_args = model_args
# learning related
self._batch_size = batch_size
self._n_iter = n_iter
self._learning_rate = learning_rate
self._l2 = l2
self._neg_samples = neg_samples
self._device = torch.device("cuda" if use_cuda else "cpu")
self.checkpoint = checkpoint
# rank evaluation related
self.test_sequence = None
self._candidate = dict()
@property
def _initialized(self):
return self._net is not None
def _initialize(self, interactions):
self._num_items = interactions.num_items
self._num_users = interactions.num_users
self.test_sequence = interactions.test_sequences
self._net = Caser(self._num_users, self._num_items, self.model_args)
self._optimizer = optim.Adam(self._net.parameters(),
weight_decay=self._l2,
lr=self._learning_rate)
def fit(self, train, test, verbose=False):
"""
The general training loop to fit the model
Parameters
----------
train: :class:`interactions.Interactions`
training instances, also contains test sequences
test: :class:`interactions.Interactions`
only contains targets for test sequences
verbose: bool, optional
print the logs
"""
# convert sequences, targets and users to numpy arrays
sequences_np = train.sequences.sequences
targets_np = train.sequences.targets
users_np = train.sequences.user_ids.reshape(-1, 1)
L, T = train.sequences.L, train.sequences.T
n_train = sequences_np.shape[0]
print('total training instances: %d' % n_train)
if not self._initialized:
self._initialize(train)
start_epoch = 1
if self.checkpoint:
print("loading checkpoint from %s" % self.checkpoint)
checkpoint = torch.load(self.checkpoint)
start_epoch = checkpoint['epoch_num']
self._net.load_state_dict(checkpoint['state_dict'])
self._optimizer.load_state_dict(checkpoint['optimizer'])
print("loaded checkpoint %s (epoch %d)" %
(self.checkpoint, start_epoch))
# compute number of parameters
print("Number of params: %d" % compute_model_size(self._net))
for epoch_num in range(start_epoch, self._n_iter + 1):
t1 = time()
# set model to training model and move it to the corresponding devices
self._net.train()
self._net = self._net.to(self._device)
users_np, sequences_np, targets_np = shuffle(
users_np, sequences_np, targets_np)
negatives_np = self._generate_negative_samples(users_np,
train,
n=self._neg_samples)
# convert numpy arrays to PyTorch tensors and move it to the corresponding devices
users, sequences, targets, negatives = (
torch.from_numpy(users_np).long(),
torch.from_numpy(sequences_np).long(),
torch.from_numpy(targets_np).long(),
torch.from_numpy(negatives_np).long())
users, sequences, targets, negatives = (users.to(self._device),
sequences.to(self._device),
targets.to(self._device),
negatives.to(self._device))
epoch_loss = 0.0
for (minibatch_num, (batch_users, batch_sequences, batch_targets,
batch_negatives)) in enumerate(
minibatch(users,
sequences,
targets,
negatives,
batch_size=self._batch_size)):
# concatenate all variables to get predictions in one run
items_to_predict = torch.cat((batch_targets, batch_negatives),
1)
items_prediction = self._net(batch_sequences, batch_users,
items_to_predict)
(targets_prediction, negatives_prediction) = torch.split(
items_prediction,
[batch_targets.size(1),
batch_negatives.size(1)],
dim=1)
self._optimizer.zero_grad()
# compute the binary cross-entropy loss
loss = sigmoid_log_loss(targets_prediction,
negatives_prediction)
epoch_loss += loss.item()
loss.backward()
self._optimizer.step()
epoch_loss /= minibatch_num + 1
t2 = time()
if verbose and epoch_num % 10 == 0:
precision, recall, ndcg, mean_aps = evaluate_ranking(
self, test, train, k=[3, 5, 10])
str_precs = "precisions=%.4f,%.4f,%.4f" % tuple(
[np.mean(a) for a in precision])
str_recalls = "recalls=%.4f,%.4f,%.4f" % tuple(
[np.mean(a) for a in recall])
str_ndcgs = "ndcgs=%.4f,%.4f,%.4f" % tuple(
[np.mean(a) for a in ndcg])
output_str = "Epoch %d [%.1f s]\tloss=%.4f, " \
"map=%.4f, %s, %s, %s[%.1f s]" % (epoch_num, t2 - t1,
epoch_loss,
mean_aps, str_precs, str_recalls, str_ndcgs,
time() - t2)
print(output_str)
else:
output_str = "Epoch %d [%.1f s]\tloss=%.4f [%.1f s]" % (
epoch_num, t2 - t1, epoch_loss, time() - t2)
print(output_str)
_save_checkpoint(
{
'epoch_num': epoch_num,
'state_dict': self._net.state_dict(),
'optimizer': self._optimizer.state_dict(),
}, 'checkpoints/gowalla-caser-dim=%d.pth.tar' % self.model_args.d)
def _generate_negative_samples(self, users, interactions, n):
"""
Sample negative from a candidate set of each user. The
candidate set of each user is defined by:
{All Items} \ {Items Rated by User}
Parameters
----------
users: array of np.int64
sequence users
interactions: :class:`interactions.Interactions`
training instances, used for generate candidates
n: int
total number of negatives to sample for each sequence
"""
users_ = users.squeeze()
negative_samples = np.zeros((users_.shape[0], n), np.int64)
if not self._candidate:
all_items = np.arange(interactions.num_items -
1) + 1 # 0 for padding
train = interactions.tocsr()
for user, row in enumerate(train):
self._candidate[user] = list(set(all_items) - set(row.indices))
for i, u in enumerate(users_):
for j in range(n):
x = self._candidate[u]
negative_samples[i, j] = x[np.random.randint(len(x))]
return negative_samples
def predict(self, user_id, item_ids=None, model=None):
"""
Make predictions for evaluation: given a user id, it will
first retrieve the test sequence associated with that user
and compute the recommendation scores for items.
Parameters
----------
user_id: int
users id for which prediction scores needed.
item_ids: array, optional
Array containing the item ids for which prediction scores
are desired. If not supplied, predictions for all items
will be computed.
"""
if self.test_sequence is None:
raise ValueError('Missing test sequences, cannot make predictions')
if model is None:
model = self._net
# set model to evaluation model
model.eval()
with torch.no_grad():
sequences_np = self.test_sequence.sequences[user_id, :]
sequences_np = np.atleast_2d(sequences_np)
if item_ids is None:
item_ids = np.arange(self._num_items).reshape(-1, 1)
sequences = torch.from_numpy(
sequences_np.astype(np.int64).reshape(1, -1))
item_ids = torch.from_numpy(item_ids.astype(np.int64))
user_id = torch.from_numpy(np.array([[user_id]]).astype(np.int64))
user, sequences, items = (user_id.to(self._device),
sequences.to(self._device),
item_ids.to(self._device))
out = model(sequences, user, items, for_pred=True)
return cpu(out.data).numpy().flatten()
class DistilledRecommender(Recommender):
"""
Contains attributes and methods that needed to train a sequential
recommendation model with ranking distillation[1]. Models are trained
by many tuples of (users, sequences, targets, negatives) and negatives
are from negative sampling: for any known tuple of (user, sequence, targets),
one or more items are randomly sampled to act as negatives.
[1] Ranking Distillation: Learning Compact Ranking Models With High
Performance for Recommender System, Jiaxi Tang and Ke Wang , KDD '18
Parameters
----------
n_iter: int,
Number of iterations to run.
batch_size: int,
Minibatch size.
l2: float,
L2 loss penalty, also known as the 'lambda' of l2 regularization.
neg_samples: int,
Number of negative samples to generate for each targets.
learning_rate: float,
Initial learning rate.
use_cuda: boolean,
Run the model on a GPU or CPU.
teacher_model_path: string,
Path to teacher's model checkpoint.
teacher_topk_path: string,
Path to teacher's top-K ranking cache for each training instance.
lamda: float
Hyperparameter for tuning the sharpness of position importance weight.
mu: float
Hyperparameter for tuning the sharpness of ranking discrepancy weight.
num_dynamic_samples: int
Number of samples used for estimating student's rank.
dynamic_start_epoch: int
Number of iteration to start using hybrid of two different weights.
K: int
Length of teacher's exemplary ranking.
teach_alpha: float:
Weight for balancing ranking loss and distillation loss.
student_model_args: args,
Student model related arguments, like latent dimensions.
teacher_model_args: args,
Teacher model related arguments, like latent dimensions.
"""
def __init__(self,
n_iter=None,
batch_size=None,
l2=None,
neg_samples=None,
learning_rate=None,
use_cuda=False,
teacher_model_path=None,
teacher_topk_path=None,
lamda=None,
mu=None,
num_dynamic_samples=None,
dynamic_start_epoch=None,
K=None,
teach_alpha=None,
student_model_args=None,
teacher_model_args=None):
# data related
self.L = None
self.T = None
# model related
self._num_items = None
self._num_users = None
self._teacher_net = None # teacher model
self._student_net = None # student model
self._student_model_args = student_model_args
self._teacher_model_args = teacher_model_args
# learning related
self._batch_size = batch_size
self._n_iter = n_iter
self._learning_rate = learning_rate
self._l2 = l2
self._neg_samples = neg_samples
self._device = torch.device("cuda" if use_cuda else "cpu")
# ranking distillation related
self._teach_alpha = teach_alpha
self._lambda = lamda
self._mu = mu
self._num_dynamic_samples = num_dynamic_samples
self._dynamic_start_epoch = dynamic_start_epoch
self._K = K
self._teacher_model_path = teacher_model_path
self._teacher_topk_path = teacher_topk_path
self._weight_renormalize = False
# rank evaluation related
self.test_sequence = None
self._candidate = dict()
@property
def _teacher_initialized(self):
return self._teacher_net is not None
def _initialize_teacher(self, interactions):
# initialize teacher model
self._num_items = interactions.num_items
self._num_users = interactions.num_users
self._teacher_net = Caser(self._num_users, self._num_items,
self._teacher_model_args)
# load teacher model
if os.path.isfile(self._teacher_model_path):
output_str = ("loading teacher model from %s" %
self._teacher_model_path)
print(output_str)
checkpoint = torch.load(self._teacher_model_path)
self._teacher_net.load_state_dict(checkpoint['state_dict'])
output_str = "loaded model %s (epoch %d)" % (
self._teacher_model_path, checkpoint['epoch_num'])
print(output_str)
else:
output_str = "no model found at %s" % self._teacher_model_path
print output_str
# set teacher model to evaluation mode
self._teacher_net.eval()
@property
def _student_initialized(self):
return self._student_net is not None
def _initialize_student(self, interactions):
self._num_items = interactions.num_items
self._num_users = interactions.num_users
self.test_sequence = interactions.test_sequences
self._student_net = Caser(self._num_users, self._num_items,
self._student_model_args)
self._optimizer = optim.Adam(self._student_net.parameters(),
weight_decay=self._l2,
lr=self._learning_rate)
def fit(self, train, test, verbose=False):
"""
The general training loop to fit the model
Parameters
----------
train: :class:`interactions.Interactions`
training instances, also contains test sequences
test: :class:`interactions.Interactions`
only contains targets for test sequences
verbose: bool, optional
print the logs
"""
# convert sequences, targets and users to numpy arrays
sequences_np = train.sequences.sequences
targets_np = train.sequences.targets
users_np = train.sequences.user_ids.reshape(-1, 1)
self.L, self.T = train.sequences.L, train.sequences.T
n_train = sequences_np.shape[0]
output_str = 'total training instances: %d' % n_train
print(output_str)
if not self._teacher_initialized:
self._initialize_teacher(train)
if not self._student_initialized:
self._initialize_student(train)
# here we compute teacher top-K ranking for each training instance in advance for faster training speed
# while we have to compute the top-K ranking on the fly if it is too large to keep in memory
if os.path.isfile(self._teacher_topk_path):
print('found teacher topk file, loading..')
teacher_ranking = np.load(self._teacher_topk_path)
else:
print('teacher topk file not found, generating.. ')
teacher_ranking = self._get_teacher_topk(sequences_np,
users_np,
targets_np,
k=self._K)
# initialize static weight (position importance weight)
weight_static = np.array(range(1, self._K + 1), dtype=np.float32)
weight_static = np.exp(-weight_static / self._lambda)
weight_static = weight_static / np.sum(weight_static)
weight_static = torch.from_numpy(weight_static).to(self._device)
weight_static = weight_static.unsqueeze(0)
# initialize dynamic weight (ranking discrepancy weight)
weight_dynamic = None
# count number of parameters
print("Number of params in teacher model: %d" %
compute_model_size(self._teacher_net))
print("Number of params in student model: %d" %
compute_model_size(self._student_net))
indices = np.arange(n_train)
start_epoch = 1
for epoch_num in range(start_epoch, self._n_iter + 1):
t1 = time()
# set teacher model to evaluation mode and move it to the corresponding devices
self._teacher_net.eval()
self._teacher_net = self._teacher_net.to(self._device)
# set student model to training mode and move it to the corresponding devices
self._student_net.train()
self._student_net = self._student_net.to(self._device)
(users_np, sequences_np,
targets_np), shuffle_indices = shuffle(users_np,
sequences_np,
targets_np,
indices=True)
indices = indices[
shuffle_indices] # keep indices for retrieval teacher's top-K ranking from cache
negatives_np = self._generate_negative_samples(users_np,
train,
n=self._neg_samples)
dynamic_samples_np = self._generate_negative_samples(
users_np, train, n=self._num_dynamic_samples)
# convert numpy arrays to PyTorch tensors and move it to the corresponding devices
users, sequences, targets, negatives = (
torch.from_numpy(users_np).long(),
torch.from_numpy(sequences_np).long(),
torch.from_numpy(targets_np).long(),
torch.from_numpy(negatives_np).long())
users, sequences, targets, negatives = (users.to(self._device),
sequences.to(self._device),
targets.to(self._device),
negatives.to(self._device))
dynamic_samples = torch.from_numpy(dynamic_samples_np).long().to(
self._device)
epoch_loss = 0.0
epoch_regular_loss = 0.0
for (minibatch_num,
(batch_indices, batch_users, batch_sequences, batch_targets,
batch_negatives, batch_dynamics)) in enumerate(
minibatch(indices,
users,
sequences,
targets,
negatives,
dynamic_samples,
batch_size=self._batch_size)):
# retrieval teacher top-K ranking given indices
batch_candidates = torch.from_numpy(
teacher_ranking[batch_indices, :]).long().to(self._device)
# concatenate all variables to get predictions in one run
items_to_predict = torch.cat(
(batch_targets, batch_negatives, batch_candidates,
batch_dynamics), 1)
items_prediction = self._student_net(batch_sequences,
batch_users,
items_to_predict)
(targets_prediction, negatives_prediction,
candidates_prediction,
dynamics_prediction) = torch.split(items_prediction, [
batch_targets.size(1),
batch_negatives.size(1),
batch_candidates.size(1),
batch_dynamics.size(1)
],
dim=1)
self._optimizer.zero_grad()
if epoch_num > self._dynamic_start_epoch:
# compute dynamic weight
dynamic_weights = list()
for col in range(self._K):
col_prediction = candidates_prediction[:,
col].unsqueeze(
1)
num_smaller_than = torch.sum(
col_prediction < dynamics_prediction,
dim=1).float()
relative_rank = num_smaller_than / self._num_dynamic_samples
predicted_rank = torch.floor(self._num_items *
relative_rank)
dynamic_weight = torch.tanh(self._mu *
(predicted_rank - col))
dynamic_weight = torch.clamp(dynamic_weight, min=0.0)
dynamic_weights.append(dynamic_weight)
weight_dynamic = torch.stack(dynamic_weights, 1)
# hybrid two weights
weight = weight_dynamic * weight_static
if self._weight_renormalize:
weight = F.normalize(weight, p=1, dim=1)
else:
weight = weight_static
# detach the weight to stop the gradient flow to the weight
weight = weight.detach()
loss, regular_loss = weighted_sigmoid_log_loss(
targets_prediction, negatives_prediction,
candidates_prediction, weight, self._teach_alpha)
epoch_loss += loss.item()
epoch_regular_loss += regular_loss.item()
loss.backward()
# assert False
self._optimizer.step()
epoch_loss /= minibatch_num + 1
epoch_regular_loss /= minibatch_num + 1
t2 = time()
if verbose and epoch_num % 10 == 0:
precision, recall, ndcg, mean_aps = evaluate_ranking(
self, test, train, k=[3, 5, 10])
str_precs = "precisions=%.4f,%.4f,%.4f" % tuple(
[np.mean(a) for a in precision])
str_recalls = "recalls=%.4f,%.4f,%.4f" % tuple(
[np.mean(a) for a in recall])
str_ndcgs = "ndcgs=%.4f,%.4f,%.4f" % tuple(
[np.mean(a) for a in ndcg])
output_str = "Epoch %d [%.1f s]\tloss=%.4f, regular_loss=%.4f, " \
"map=%.4f, %s, %s, %s[%.1f s]" % (epoch_num, t2 - t1,
epoch_loss, epoch_regular_loss,
mean_aps, str_precs, str_recalls, str_ndcgs,
time() - t2)
print(output_str)
else:
output_str = "Epoch %d [%.1f s]\tloss=%.4f, regular_loss=%.4f[%.1f s]" % (
epoch_num, t2 - t1, epoch_loss, epoch_regular_loss,
time() - t2)
print(output_str)
def _get_teacher_topk(self, sequences, users, targets, k):
"""
Pre-compute and cache teacher's top-K ranking for each training instance.
By doing this we can make training with distillation much faster.
Parameters
----------
sequences: array of np.int64
sequencces of items
users: array of np.int64
users associated with each sequence
targets: array of np.int64
target item that user interact with given the sequence
k: int
length of teacher's exemplary ranking
"""
with_targets = False
n_train = sequences.shape[0]
indices = np.arange(n_train)
users, sequences = torch.from_numpy(users).long(), torch.from_numpy(
sequences).long()
# teacher topk results
teacher_topk = np.zeros((n_train, k), dtype=np.int64)
for (batch_indices, batch_users, batch_sequences,
batch_targets) in minibatch(indices,
users,
sequences,
targets,
batch_size=16):
cur_batch_size = batch_users.shape[0]
all_items = torch.arange(start=0, end=self._num_items).repeat(
cur_batch_size, 1).long()
teacher_prediction = self._teacher_net(batch_sequences,
batch_users,
all_items).detach()
_, tops = teacher_prediction.topk(
k * 2, dim=1) # return the topk by column
tops = tops.cpu().numpy()
new_tops = np.concatenate((batch_targets, tops), axis=1)
topks = np.zeros((cur_batch_size, k), dtype=np.int64)
for i, row in enumerate(new_tops):
_, idx = np.unique(row, return_index=True)
# whether teacher's top-k ranking consider target items
if with_targets:
topk = row[np.sort(idx)][:k]
else:
topk = row[np.sort(idx)][self.T:k + self.T]
topks[i, :] = topk
teacher_topk[batch_indices, :] = topks
np.save(
'gowalla-teacher-dim=%d-top=%d.npy' %
(self._teacher_model_args.d, k), teacher_topk)
return teacher_topk
def predict(self, user_id, item_ids=None, model=None):
return super(DistilledRecommender,
self).predict(user_id, item_ids, model=self._student_net)