title: Get sum total for each column in d3.js
body: <p>I am looking forward to get the sum total of each column using d3.js in a dynamic way. Please find the example-</p>
  
  <pre>
  key  | value1 | value2 | value3 | value4 
  -----+--------+--------+--------+--------
  mike | 1      | 3      | 5      | 7      
  -----+--------+--------+--------+--------
  mila | 2      | 4      | 6      | 8
  -----+--------+--------+--------+--------
  minda| 9      | 11     | 13     | 15
  </pre>
  
  <p>Here, sum total for value1 is 12, value2 is 18. I need the sum for each of the column in a dynamic way. </p>