Source code for recbole.model.sequential_recommender.sasrec

# -*- coding: utf-8 -*-
# @Time    : 2020/9/18 11:33
# @Author  : Hui Wang
# @Email   : hui.wang@ruc.edu.cn

"""
SASRec
################################################

Reference:
    Wang-Cheng Kang et al. "Self-Attentive Sequential Recommendation." in ICDM 2018.

Reference:
    https://github.com/kang205/SASRec

"""

import torch
from torch import nn

from recbole.model.abstract_recommender import SequentialRecommender
from recbole.model.layers import TransformerEncoder
from recbole.model.loss import BPRLoss


[docs]class SASRec(SequentialRecommender): r""" SASRec is the first sequential recommender based on self-attentive mechanism. NOTE: In the author's implementation, the Point-Wise Feed-Forward Network (PFFN) is implemented by CNN with 1x1 kernel. In this implementation, we follows the original BERT implementation using Fully Connected Layer to implement the PFFN. """ def __init__(self, config, dataset): super(SASRec, self).__init__(config, dataset) # load parameters info self.n_layers = config['n_layers'] self.n_heads = config['n_heads'] self.hidden_size = config['hidden_size'] # same as embedding_size self.inner_size = config['inner_size'] # the dimensionality in feed-forward layer self.hidden_dropout_prob = config['hidden_dropout_prob'] self.attn_dropout_prob = config['attn_dropout_prob'] self.hidden_act = config['hidden_act'] self.layer_norm_eps = config['layer_norm_eps'] self.initializer_range = config['initializer_range'] self.loss_type = config['loss_type'] # define layers and loss self.item_embedding = nn.Embedding(self.n_items, self.hidden_size, padding_idx=0) self.position_embedding = nn.Embedding(self.max_seq_length, self.hidden_size) self.trm_encoder = TransformerEncoder( n_layers=self.n_layers, n_heads=self.n_heads, hidden_size=self.hidden_size, inner_size=self.inner_size, hidden_dropout_prob=self.hidden_dropout_prob, attn_dropout_prob=self.attn_dropout_prob, hidden_act=self.hidden_act, layer_norm_eps=self.layer_norm_eps ) self.LayerNorm = nn.LayerNorm(self.hidden_size, eps=self.layer_norm_eps) self.dropout = nn.Dropout(self.hidden_dropout_prob) if self.loss_type == 'BPR': self.loss_fct = BPRLoss() elif self.loss_type == 'CE': self.loss_fct = nn.CrossEntropyLoss() else: raise NotImplementedError("Make sure 'loss_type' in ['BPR', 'CE']!") # parameters initialization self.apply(self._init_weights) def _init_weights(self, module): """ Initialize the weights """ if isinstance(module, (nn.Linear, nn.Embedding)): # Slightly different from the TF version which uses truncated_normal for initialization # cf https://github.com/pytorch/pytorch/pull/5617 module.weight.data.normal_(mean=0.0, std=self.initializer_range) elif isinstance(module, nn.LayerNorm): module.bias.data.zero_() module.weight.data.fill_(1.0) if isinstance(module, nn.Linear) and module.bias is not None: module.bias.data.zero_()
[docs] def get_attention_mask(self, item_seq): """Generate left-to-right uni-directional attention mask for multi-head attention.""" attention_mask = (item_seq > 0).long() extended_attention_mask = attention_mask.unsqueeze(1).unsqueeze(2) # torch.int64 # mask for left-to-right unidirectional max_len = attention_mask.size(-1) attn_shape = (1, max_len, max_len) subsequent_mask = torch.triu(torch.ones(attn_shape), diagonal=1) # torch.uint8 subsequent_mask = (subsequent_mask == 0).unsqueeze(1) subsequent_mask = subsequent_mask.long().to(item_seq.device) extended_attention_mask = extended_attention_mask * subsequent_mask extended_attention_mask = extended_attention_mask.to(dtype=next(self.parameters()).dtype) # fp16 compatibility extended_attention_mask = (1.0 - extended_attention_mask) * -10000.0 return extended_attention_mask
[docs] def forward(self, item_seq, item_seq_len): position_ids = torch.arange(item_seq.size(1), dtype=torch.long, device=item_seq.device) position_ids = position_ids.unsqueeze(0).expand_as(item_seq) position_embedding = self.position_embedding(position_ids) item_emb = self.item_embedding(item_seq) input_emb = item_emb + position_embedding input_emb = self.LayerNorm(input_emb) input_emb = self.dropout(input_emb) extended_attention_mask = self.get_attention_mask(item_seq) trm_output = self.trm_encoder(input_emb, extended_attention_mask, output_all_encoded_layers=True) output = trm_output[-1] output = self.gather_indexes(output, item_seq_len - 1) return output # [B H]
[docs] def calculate_loss(self, interaction): item_seq = interaction[self.ITEM_SEQ] item_seq_len = interaction[self.ITEM_SEQ_LEN] seq_output = self.forward(item_seq, item_seq_len) pos_items = interaction[self.POS_ITEM_ID] if self.loss_type == 'BPR': neg_items = interaction[self.NEG_ITEM_ID] pos_items_emb = self.item_embedding(pos_items) neg_items_emb = self.item_embedding(neg_items) pos_score = torch.sum(seq_output * pos_items_emb, dim=-1) # [B] neg_score = torch.sum(seq_output * neg_items_emb, dim=-1) # [B] loss = self.loss_fct(pos_score, neg_score) return loss else: # self.loss_type = 'CE' test_item_emb = self.item_embedding.weight logits = torch.matmul(seq_output, test_item_emb.transpose(0, 1)) loss = self.loss_fct(logits, pos_items) return loss
[docs] def predict(self, interaction): item_seq = interaction[self.ITEM_SEQ] item_seq_len = interaction[self.ITEM_SEQ_LEN] test_item = interaction[self.ITEM_ID] seq_output = self.forward(item_seq, item_seq_len) test_item_emb = self.item_embedding(test_item) scores = torch.mul(seq_output, test_item_emb).sum(dim=1) # [B] return scores
[docs] def full_sort_predict(self, interaction): item_seq = interaction[self.ITEM_SEQ] item_seq_len = interaction[self.ITEM_SEQ_LEN] seq_output = self.forward(item_seq, item_seq_len) test_items_emb = self.item_embedding.weight scores = torch.matmul(seq_output, test_items_emb.transpose(0, 1)) # [B n_items] return scores