title: Find Indices Of Columns Having Some Nonzero Element In A 2d array
body: <p>I have a numpy array with dim (157,1944).</p>
  
  <p>I want to get indices of columns that have a Nonzero element in any row. </p>
  
  <p>example: <code>[[0,0,3,4], [0,0,1,1]]</code> ----> <code>[2,3]</code></p>
  
  <p>If you look each row, there is a Non Zero element in columns [2, 3]</p>
  
  <p>So if I have </p>
  
  <p><code>[[0,1,3,4], [0,0,1,1]]</code></p>
  
  <p>I should get <code>[1,2,3]</code> because column index 0 has no Nonzero elements in any row.</p>