仅当#terms> 3000时,DocumentTermMatrix才会出现奇怪的错误

Question

我的下面的代码工作正常,除非我使用创建一个超过3000个术语的DocumentTermMatrix.这一行:

movie_dict <- findFreqTerms(movie_dtm_train, 8)
movie_dtm_hiFq_train <- DocumentTermMatrix(movie_corpus_train, list(dictionary = movie_dict))

失败:

Error in simple_triplet_matrix(i = i, j = j, v = as.numeric(v), nrow = length(allTerms),  : 
  'i, j, v' different lengths
In addition: Warning messages:
1: In mclapply(unname(content(x)), termFreq, control) :
  all scheduled cores encountered errors in user code
2: In simple_triplet_matrix(i = i, j = j, v = as.numeric(v), nrow = length(allTerms),  :
  NAs introduced by coercion

有什么方法可以解决这个问题吗？对于DocumentTermMatrix,3000*60000矩阵是否太大了？这对于文档分类来说似乎相当小..

完整代码段:

n1 <- 60000
n2 <- 70000
#******* loading the data ******************************************
#kaggle sentiment_analysis dataset    
movie_all <- read.delim('train.tsv', stringsAsFactors=FALSE)
movie_raw <- movie_all[1:(n2),]

#******* cleaning the corpus ***************************************
movie_corpus <- Corpus(VectorSource(movie_raw$Phrase))
movie_corpus_clean <- tm_map(movie_corpus, content_transformer(tolower))
movie_corpus_clean <- tm_map(movie_corpus_clean, removeNumbers)
movie_corpus_clean <- tm_map(movie_corpus_clean, removeWords, stopwords())
movie_corpus_clean <- tm_map(movie_corpus_clean, removePunctuation)
movie_corpus_clean <- tm_map(movie_corpus_clean, stripWhitespace)
movie_dtm <- DocumentTermMatrix(movie_corpus_clean)

#*********** break out data into train/test sets *******************
movie_train <- movie_raw[1:(n1),]
movie_corpus_train <- movie_corpus_clean[1:(n1)]
movie_dtm_train <- movie_dtm[1:(n1),]

#*********** remove rare words from document term matrix ***********
movie_dict <- findFreqTerms(movie_dtm_train, 8)
movie_dtm_hiFq_train <- DocumentTermMatrix(movie_corpus_train, list(dictionary = movie_dict))

编辑 失败:

movie_dtm_hiFq_train <- DocumentTermMatrix(movie_corpus_train[1:60000], list(dictionary = movie_dict))

但这有效:

d1 <- DocumentTermMatrix(movie_corpus_train[1:30000], list(dictionary = movie_dict))
d2 <- DocumentTermMatrix(movie_corpus_train[30000:60000], list(dictionary = movie_dict))
movie_dtm_hiFq_train <- c(d1, d2)

这让我相信这一定是一个尺寸问题..