title: convert array element from string to number
body: <p>I've some numbers which come from a query and that I have to represent using the json_encode function.
  Everything work but the output looks like this</p>
  
  <pre><code>{ "label": "man", "data":[["0","1.13"], ["1","1.38"], ["2","1.87"], ["3","1.12"], ["4","1.28"]]}
  </code></pre>
  
  <p>so I think that the problem is that all the numbers are stored as string.
  Is there a function to convert all the elements in number?</p>