Document-term matrix in R - bigram tokenizer not working

Question

I am trying to make 2 document-term matrices for a corpus, one with unigrams and one with bigrams. However, the bigram matrix is currently just identical to the unigram matrix, and I'm not sure why.

The code:

docs<-Corpus(DirSource("data", recursive=TRUE))

# Get the document term matrices
BigramTokenizer <- function(x) NGramTokenizer(x, Weka_control(min = 2, max = 2))
dtm_unigram <- DocumentTermMatrix(docs, control = list(tokenize="words", 
    removePunctuation = TRUE, 
    stopwords = stopwords("english"), 
    stemming = TRUE))
dtm_bigram <- DocumentTermMatrix(docs, control = list(tokenize = BigramTokenizer,
    removePunctuation = TRUE,
    stopwords = stopwords("english"),
    stemming = TRUE))

inspect(dtm_unigram)
inspect(dtm_bigram)

I also tried using ngram(x, n=2) from the ngram package as the tokenizer, but that doesn't work either. How do I fix the bigram tokenization?

Answer 1

The tokenizer option doesn't seem to work with Corpus (SimpleCorpus). Using VCorpus instead cleared up the problem.