我有这个数据处理:
library(text2vec)
##Using perplexity for hold out set
t1 <- Sys.time()
perplex <- c()
for (i in 3:25){
set.seed(17)
lda_model2 <- LDA$new(n_topics = i)
doc_topic_distr2 <- lda_model2$fit_transform(x = dtm, progressbar = F)
set.seed(17)
sample.dtm2 <- itoken(rawsample$Abstract,
preprocessor = prep_fun,
tokenizer = tok_fun,
ids = rawsample$id,
progressbar = F) %>%
create_dtm(vectorizer,vtype = "dgTMatrix", progressbar = FALSE)
set.seed(17)
new_doc_topic_distr2 <- lda_model2$transform(sample.dtm2, n_iter = 1000,
convergence_tol = 0.001, n_check_convergence = 25,
progressbar = FALSE)
perplex[i] <- text2vec::perplexity(sample.dtm2, topic_word_distribution =
lda_model2$topic_word_distribution,
doc_topic_distribution = new_doc_topic_distr2)
}
print(difftime(Sys.time(), t1, units = 'sec'))
我知道有很多这样的问题,但我一直无法准确找到我的情况的答案。在上图中,您可以看到潜在狄利克雷分配模型从 3 到 25 个主题编号的困惑度计算。我想获得其中最充分的值,这意味着我想找到肘部或膝盖,对于那些可能只被视为简单数字向量的值,其结果如下所示:
1 NA
2 NA
3 222.6229
4 210.3442
5 200.1335
6 190.3143
7 180.4195
8 174.2634
9 166.2670
10 159.7535
11 153.7785
12 148.1623
13 144.1554
14 141.8250
15 138.8301
16 134.4956
17 131.0745
18 128.8941
19 125.8468
20 123.8477
21 120.5155
22 118.4426
23 116.4619
24 113.2401
25 114.1233
plot(perplex)
我会说肘部是 13 或 16,但我不完全确定,我想要确切的数字作为结果。我在这篇论文中看到 f''(x) / (1+f'(x)^2)^1.5 是膝盖公式,我这样尝试并说它是 18:
> d1 <- diff(perplex) # first derivative
> d2 <- diff(d1) / diff(perplex[-1]) # second derivative
> knee <- (d2)/((1+(d1)^2)^1.5)
Warning message:
In (d2)/((1 + (d1)^2)^1.5) :
longer object length is not a multiple of shorter object length
> which.min(knee)
[1] 18
我无法完全弄清楚这件事。有人想分享我如何根据困惑作为结果获得确切的理想主题编号吗?