paddlenlp.metrics.bleu 源代码

# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.

import math
import sys
from collections import defaultdict

import paddle

from .utils import default_trans_func

__all__ = ["BLEU", "BLEUForDuReader"]

def get_match_size(cand_ngram, refs_ngram):
    ref_set = defaultdict(int)
    for ref_ngram in refs_ngram:
        tmp_ref_set = defaultdict(int)
        for ngram in ref_ngram:
            tmp_ref_set[tuple(ngram)] += 1
        for ngram, count in tmp_ref_set.items():
            ref_set[tuple(ngram)] = max(ref_set[tuple(ngram)], count)
    cand_set = defaultdict(int)
    for ngram in cand_ngram:
        cand_set[tuple(ngram)] += 1
    match_size = 0
    for ngram, count in cand_set.items():
        match_size += min(count, ref_set.get(tuple(ngram), 0))
    cand_size = len(cand_ngram)
    return match_size, cand_size

def get_ngram(sent, n_size, label=None):
    def _ngram(sent, n_size):
        ngram_list = []
        for left in range(len(sent) - n_size):
            ngram_list.append(sent[left:left + n_size + 1])
        return ngram_list

    ngram_list = _ngram(sent, n_size)
    if label is not None:
        ngram_list = [ngram + '_' + label for ngram in ngram_list]
    return ngram_list

[文档]class BLEU(paddle.metric.Metric): r''' BLEU (bilingual evaluation understudy) is an algorithm for evaluating the quality of text which has been machine-translated from one natural language to another. This metric uses a modified form of precision to compare a candidate translation against multiple reference translations. BLEU could be used as `paddle.metric.Metric` class, or an ordinary class. When BLEU is used as `paddle.metric.Metric` class. A function is needed that transforms the network output to reference string list, and transforms the label to candidate string. By default, a default function `default_trans_func` is provided, which gets target sequence id by calculating the maximum probability of each step. In this case, user must provide `vocab`. It should be noted that the BLEU here is different from the BLEU calculated in prediction, and it is only for observation during training and evaluation. .. math:: BP & = \begin{cases} 1, & \text{if }c>r \\ e_{1-r/c}, & \text{if }c\leq r \end{cases} BLEU & = BP\exp(\sum_{n=1}^N w_{n} \log{p_{n}}) where `c` is the length of candidate sentence, and `r` is the length of reference sentence. Args: trans_func (callable, optional): `trans_func` transforms the network output to string to calculate. vocab (dict|, optional): Vocab for target language. If `trans_func` is None and BLEU is used as `paddle.metric.Metric` instance, `default_trans_func` will be performed and `vocab` must be provided. n_size (int, optional): Number of gram for BLEU metric. Defaults to 4. weights (list, optional): The weights of precision of each gram. Defaults to None. name (str, optional): Name of `paddle.metric.Metric` instance. Defaults to "bleu". Examples: 1. Using as a general evaluation object. .. code-block:: python from paddlenlp.metrics import BLEU bleu = BLEU() cand = ["The","cat","The","cat","on","the","mat"] ref_list = [["The","cat","is","on","the","mat"], ["There","is","a","cat","on","the","mat"]] bleu.add_inst(cand, ref_list) print(bleu.score()) # 0.4671379777282001 2. Using as an instance of `paddle.metric.Metric`. .. code-block:: python # You could add the code below to Seq2Seq example in this repo to # use BLEU as `paddlenlp.metric.Metric' class. If you run the # following code alone, you may get an error. # log example: # Epoch 1/12 # step 100/507 - loss: 308.7948 - Perplexity: 541.5600 - bleu: 2.2089e-79 - 923ms/step # step 200/507 - loss: 264.2914 - Perplexity: 334.5099 - bleu: 0.0093 - 865ms/step # step 300/507 - loss: 236.3913 - Perplexity: 213.2553 - bleu: 0.0244 - 849ms/step from import Vocab from paddlenlp.metrics import BLEU bleu_metric = BLEU(vocab=src_vocab.idx_to_token) model.prepare(optimizer, CrossEntropyCriterion(), [ppl_metric, bleu_metric]) ''' def __init__(self, trans_func=None, vocab=None, n_size=4, weights=None, name="bleu"): super(BLEU, self).__init__() if not weights: weights = [1 / n_size for _ in range(n_size)] assert len(weights) == n_size, ( "Number of weights and n-gram should be the same, got Number of weights: '%d' and n-gram: '%d'" % (len(weights), n_size)) self._name = name self.match_ngram = {} self.candi_ngram = {} self.weights = weights self.bp_r = 0 self.bp_c = 0 self.n_size = n_size self.vocab = vocab self.trans_func = trans_func
[文档] def update(self, output, label, seq_mask=None): if self.trans_func is None: if self.vocab is None: raise AttributeError( "The `update` method requires users to provide `trans_func` or `vocab` when initializing BLEU." ) cand_list, ref_list = default_trans_func( output, label, seq_mask=seq_mask, vocab=self.vocab) else: cand_list, ref_list = self.trans_func(output, label, seq_mask) if len(cand_list) != len(ref_list): raise ValueError( "Length error! Please check the output of network.") for i in range(len(cand_list)): self.add_inst(cand_list[i], ref_list[i])
[文档] def add_inst(self, cand, ref_list): ''' Update the states based on a pair of candidate and references. Args: cand (list): Tokenized candidate sentence. ref_list (list of list): List of tokenized ground truth sentences. ''' for n_size in range(self.n_size): self.count_ngram(cand, ref_list, n_size) self.count_bp(cand, ref_list)
def count_ngram(self, cand, ref_list, n_size): cand_ngram = get_ngram(cand, n_size) refs_ngram = [] for ref in ref_list: refs_ngram.append(get_ngram(ref, n_size)) if n_size not in self.match_ngram: self.match_ngram[n_size] = 0 self.candi_ngram[n_size] = 0 match_size, cand_size = get_match_size(cand_ngram, refs_ngram) self.match_ngram[n_size] += match_size self.candi_ngram[n_size] += cand_size def count_bp(self, cand, ref_list): self.bp_c += len(cand) self.bp_r += min([(abs(len(cand) - len(ref)), len(ref)) for ref in ref_list])[1]
[文档] def reset(self): self.match_ngram = {} self.candi_ngram = {} self.bp_r = 0 self.bp_c = 0
[文档] def accumulate(self): ''' Calculates and returns the final bleu metric. Returns: Tensor: Returns the accumulated metric `bleu` and its data type is float64. ''' prob_list = [] for n_size in range(self.n_size): try: if self.candi_ngram[n_size] == 0: _score = 0.0 else: _score = self.match_ngram[n_size] / float(self.candi_ngram[ n_size]) except: _score = 0 if _score == 0: _score = sys.float_info.min prob_list.append(_score) logs = math.fsum(w_i * math.log(p_i) for w_i, p_i in zip(self.weights, prob_list)) bp = math.exp(min(1 - self.bp_r / float(self.bp_c), 0)) bleu = bp * math.exp(logs) return bleu
def score(self): return self.accumulate()
[文档] def name(self): return self._name
[文档]class BLEUForDuReader(BLEU): ''' BLEU metric with bonus for DuReader contest. Please refer to `DuReader Homepage<>`_ for more details. Args: n_size (int, optional): Number of gram for BLEU metric. Defaults to 4. alpha (float, optional): Weight of YesNo dataset when adding bonus for DuReader contest. Defaults to 1.0. beta (float, optional): Weight of Entity dataset when adding bonus for DuReader contest. Defaults to 1.0. ''' def __init__(self, n_size=4, alpha=1.0, beta=1.0): super(BLEUForDuReader, self).__init__(n_size) self.alpha = alpha self.beta = beta
[文档] def add_inst(self, cand, ref_list, yn_label=None, yn_ref=None, entity_ref=None): BLEU.add_inst(self, cand, ref_list) if yn_label is not None and yn_ref is not None: self.add_yn_bonus(cand, ref_list, yn_label, yn_ref) elif entity_ref is not None: self.add_entity_bonus(cand, entity_ref)
def add_yn_bonus(self, cand, ref_list, yn_label, yn_ref): for n_size in range(self.n_size): cand_ngram = get_ngram(cand, n_size, label=yn_label) ref_ngram = [] for ref_id, r in enumerate(yn_ref): ref_ngram.append(get_ngram(ref_list[ref_id], n_size, label=r)) match_size, cand_size = get_match_size(cand_ngram, ref_ngram) self.match_ngram[n_size] += self.alpha * match_size self.candi_ngram[n_size] += self.alpha * match_size def add_entity_bonus(self, cand, entity_ref): for n_size in range(self.n_size): cand_ngram = get_ngram(cand, n_size, label='ENTITY') ref_ngram = [] for reff_id, r in enumerate(entity_ref): ref_ngram.append(get_ngram(r, n_size, label='ENTITY')) match_size, cand_size = get_match_size(cand_ngram, ref_ngram) self.match_ngram[n_size] += self.beta * match_size self.candi_ngram[n_size] += self.beta * match_size