python - NLTK 困惑度测度反演

Question

我已经给出了训练文本和测试文本。我想做的是通过训练数据训练语言模型来计算测试数据的困惑度。

这是我的代码:

import os
import requests
import io #codecs
from nltk.util import everygrams
from nltk.lm.preprocessing import pad_both_ends

from nltk import word_tokenize, sent_tokenize 

fileTest = open("AaronPressman.txt","r");
with io.open('AaronPressman.txt', encoding='utf8') as fin:
        textTest = fin.read()
if os.path.isfile('AaronPressmanEdited.txt'):
    with io.open('AaronPressmanEdited.txt', encoding='utf8') as fin:
        text = fin.read()

# Tokenize the text.
tokenized_text = [list(map(str.lower, word_tokenize(sent))) 
                for sent in sent_tokenize(text)]

from nltk.lm.preprocessing import padded_everygram_pipeline
from nltk.lm import Laplace

n = 1
padded_bigrams = list(pad_both_ends(word_tokenize(textTest), n=1))
trainTest = everygrams(padded_bigrams, min_len = n , max_len=n);

train_data, padded_sents = padded_everygram_pipeline(n, tokenized_text)


model = Laplace(n) 
model.fit(train_data, padded_sents)

print(model.perplexity(trainTest)) 

当我使用 n=1(即一元语法)运行此代码时，我得到“1068.332393940235”。当 n=2 或二元组时，我得到 "1644.3441077259993"，对于三元组，我得到 2552.2085752565313。

它有什么问题吗？

Answer 1

您创建测试数据的方式是错误的(小写火车数据，但测试数据未转换为小写。测试数据中缺少开始和结束标记)。试试这个

import os
import requests
import io #codecs
from nltk.util import everygrams
from nltk.lm.preprocessing import pad_both_ends
from nltk.lm.preprocessing import padded_everygram_pipeline
from nltk.lm import Laplace
from nltk import word_tokenize, sent_tokenize 

"""
fileTest = open("AaronPressman.txt","r");
with io.open('AaronPressman.txt', encoding='utf8') as fin:
        textTest = fin.read()
if os.path.isfile('AaronPressmanEdited.txt'):
    with io.open('AaronPressmanEdited.txt', encoding='utf8') as fin:
        text = fin.read()
"""
textTest = "This is an ant. This is a cat"
text = "This is an orange. This is a mango"

n = 2
# Tokenize the text.
tokenized_text = [list(map(str.lower, word_tokenize(sent))) 
                for sent in sent_tokenize(text)]
train_data, padded_sents = padded_everygram_pipeline(n, tokenized_text)

tokenized_text = [list(map(str.lower, word_tokenize(sent))) 
                for sent in sent_tokenize(textTest)]
test_data, padded_sents = padded_everygram_pipeline(n, tokenized_text)

model = Laplace(1) 
model.fit(train_data, padded_sents)

s = 0
for i, test in enumerate(test_data):
    p = model.perplexity(test)
    s += p

print ("Perplexity: {0}".format(s/(i+1)))