title: Does tm package itself provide a built-in way to combine document-term matrices?
body: <p>Does tm package itself provide a built-in way to combine document-term matrices? </p>
  
  <p>I generated 4 document term matrices on the same corpus, each for 1,2,3,4 gram. They are all really big: 200k*10k so converting them into data frames and then cbinding them is out of question. I know I could write a program recording the non-zero elements in each of the matrices and build a sparse-matrix, but that is a lot of trouble. It just seems natural for tm package to provide this functionality. So if it does,I don't want to rebuild something that has already been built.</p>
  
  <p>If it doesn't, is there any handier way to combine dtms than writing a program to record indices of non-zero elements of dtms and then making a sparse matrix?</p>