title: how can I combine multiple sparse and dense matrices together
body: <p>I've been working with some text data and I've got few sparse matrices and dense (numpy arrays). I just want to know how to combine them correctly.</p>
  
  <p>These are the types and shape of the arrays:</p>
  
  <pre><code>list1 
  &lt;109248x9 sparse matrix of type '&lt;class 'numpy.int64'&gt;'
      with 152643 stored elements in Compressed Sparse Row format&gt;
  
  list2
  &lt;109248x3141 sparse matrix of type '&lt;class 'numpy.int64'&gt;'
      with 350145 stored elements in Compressed Sparse Row format&gt;
  
  list3.shape   ,  type(list3)
  (109248, 300) ,  numpy.ndarray
  
  list4.shape   ,  type
  (109248, 51)  ,  numpy.ndarray
  </code></pre>
  
  <p>I just want to combine all of them together as one dense matrix. I tried some vstack and hstack but couldn't figure it out. Any help is much appreciated.</p>
  
  <pre><code>Output required: (109248, 3501)
  </code></pre>