title: sparse 3d matrix/array in Python?
body: <p>In scipy, we can construct a sparse matrix using scipy.sparse.lil_matrix() etc. But the matrix is in 2d.</p>
  
  <p>I am wondering if there is an existing data structure for sparse 3d matrix / array (tensor) in Python?</p>
  
  <p>p.s. I have lots of sparse data in 3d and need a tensor to store / perform multiplication. Any suggestions to implement such a tensor if there's no existing data structure?</p>