title: calculate precision and recall in a confusion matrix
body: <p>Suppose I have a confusion matrix as like as below. How can I calculate precision and recall?</p>
  
  <p><a href="https://i.stack.imgur.com/PbN8J.png" rel="noreferrer"><img src="https://i.stack.imgur.com/PbN8J.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/yb5aC.png" rel="noreferrer"><img src="https://i.stack.imgur.com/yb5aC.png" alt="enter image description here"></a></p>