title: Numpy method to return the index of the occurrence of an array within an array of arrays
body: <p>I have an array of arrays that represents a set of unique colour values:</p>
  
  <pre><code>[[0.         0.         0.        ]
   [0.         0.         1.        ]
   [0.         1.         1.        ]
   [0.5019608  0.5019608  0.5019608 ]
   [0.64705884 0.16470589 0.16470589]
   [0.9607843  0.9607843  0.8627451 ]
   [1.         0.         0.        ]
   [1.         0.84313726 0.        ]
   [1.         1.         0.        ]
   [1.         1.         1.        ]]
  </code></pre>
  
  <p>And another numpy array that represents one of the colours:</p>
  
  <pre><code>[0.9607843  0.9607843  0.8627451 ]
  </code></pre>
  
  <p>I need a function to find the index where the colour array occurs in the set of colours, i.e. the function should return 5 for the arrays above. </p>