title: How to turn a list of lists to a sparse matrix in R without using lapply?
body: <p>I have a list of lists resulting from a bigsplit() operation (from package biganalytics, part of the bigmemory packages).</p>
  
  <p>Each list represents a column in a matrix, and each list item is an index to a value of 1 in a binary matrix.</p>
  
  <p>What is the best way to turn this list into a sparse binary (0/1) matrix?
  Is using lapply() within an lapply() the only solution? How do I keep the factors naming the lists as names for the columns?</p>