Value between 0 and 1 indicating the proportion of documents
with no occurrences of a term above which that term should be dropped. By default
all terms are kept (sparsity=1).
dictionary
A vector of terms to which the matrix should be restricted.
By default, all words with more than min_length characters are considered.
remove_stopwords
Whether to remove stopwords appearing in a language-specific list
(see tm::stopwords).
tolower
Whether to convert all text to lower case.
remove_punctuation
Whether to remove all punctuation from text before
tokenizing terms.
remove_numbers
Whether to remove all numbers from text before
tokenizing terms.
min_length
The minimal number of characters for a word to be retained.