title: Extract different rows from two numpy 2D arrays
body: <p>I generated a new random rows matrix B (50, 40) from a matrix A (100, 40):</p>
  
  <pre><code>B = A[np.random.randint(0,100,size=50)]  # it works fine.
  </code></pre>
  
  <p>Now, I want to take the rows from A that isn't in matrix B.</p>
  
  <pre><code>C = A not in B   # pseudocode.
  </code></pre>