title: how we apply xor in php array
body: <p><strong>hot deck imputation algoritm:</strong> 
  for each object that contains missing values the most similar object (according to some distance function) is found, and the missing values are imputed from that object
  if the most similar record also contains missing values for the same feature then it is discarded and another closest object is found
  the procedure is repeated until all the missing values are imputed 
  when no similar object is found, the closest object with the minimum number of missing values is chosen to impute the missing values 
  <strong>bellow the table contain missing values</strong></p>
  
  <p><a href="https://i.stack.imgur.com/WHNfa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WHNfa.png" alt="enter image description here"></a></p>
  
  <p>the missing value fill bellow the table using xor operation</p>
  
  <p><a href="https://i.stack.imgur.com/zyU2c.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zyU2c.png" alt="enter image description here"></a></p>
  
  <p>if the 1st object contain null value the we compare this object to all other rows and count distance and found shortest distance then put the missing values</p>