title: Highcharts not picking up on date - dates being interpreted as strings
body: <p>I'm trying to create a highchart with irregular x axis, a bit like this: <a href="http://jsfiddle.net/gh/get/jquery/1.9.1/highslide-software/highcharts.com/tree/master/samples/highcharts/demo/spline-irregular-time/" rel="nofollow noreferrer">http://jsfiddle.net/gh/get/jquery/1.9.1/highslide-software/highcharts.com/tree/master/samples/highcharts/demo/spline-irregular-time/</a></p>
  
  <p>I'm pulling my data from mySQL via PHP and processing in JSON format.</p>
  
  <p>I can't get highcharts/JS to read the dates in date format - it seems to be pulling them as strings.</p>
  
  <p>Here's my script:</p>
  
  <pre><code>$(document).ready(function() {
      var options = {
          chart: {
              type: 'spline',
              marginRight: 130,
              marginBottom: 25
          },
          title: {
              text: 'some title',
              x: -20 //center
          },
          subtitle: {
              text: '',
              x: -20
          },
          xAxis: {
              type: 'datetime',
              dateTimeLabelFormats: { // don't display the dummy year
                  month: '%e. %b',
                  year: '%b'
              },
              categories: []
          },
          yAxis: {
              title: {
                  text: 'L/min'
              },
              plotLines: [{
                  value: 0,
                  width: 1,
                  color: '#808080'
              }]
          },
          plotOptions: {
              spline: {
                  marker: {
                      enabled: true
                  }
              }
          },
  
          tooltip: {
              formatter: function() {
                  return '&lt;b&gt;'+ this.series.name +': '+
                  this.y +'&lt;/b&gt;&lt;br&gt;'+ this.x;
              }
          },
          legend: {
              layout: 'vertical',
              align: 'right',
              verticalAlign: 'top',
              x: -10,
              y: 100,
              borderWidth: 0
          },
          series: []
      }
  
          $.getJSON("allreports/report.php", function(json) {
  
          options.xAxis.categories = json[0]['data'];
          options.series[0] = json[1];
          options.chart.renderTo = 'container';
          chart = new Highcharts.Chart(options);
      });
  </code></pre>
  
  <p>and here's my PHP page:</p>
  
  <pre><code>&lt;?php
      $con = mysql_connect("localhost","db-user","db-pw");
  
      if (!$con) {
          die('Could not connect: ' . mysql_error());
      }
  
      mysql_select_db("db", $con);
  
      $sth = mysql_query("SELECT v1,v2 FROM table");
      $rows = array();
      $rows['name'] = 'v1';
      while($r = mysql_fetch_array($sth)) {
          $rows['data'][] = $r['v1'];
      }
  
      $result = array();
      array_push($result,$rows1);
      array_push($result,$rows);
  
  
      print json_encode($result, JSON_NUMERIC_CHECK);
  
  
      mysql_close($con);
  ?&gt;
  </code></pre>
  
  <p>This outputs the following:</p>
  
  <pre><code>[{"name":"medicinetime","data":["01,01,1970,01,00,00","01,01,1970,01,33,36","01,01,1970,01,33,36","01,01,1970,01,33,36"]},{"name":"units","data":[1,3,2,2]}]
  </code></pre>
  
  <p>But my chart is as follows:</p>
  
  <p><a href="https://i.stack.imgur.com/mskiN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mskiN.png" alt="output"></a></p>
  
  <p>Any thoughts on what I'm doing wrong please? What do I need to do to get PHP/JS to pick up on this array as a series of datetimes rather than strings?</p>
  
  <p>Thank you!</p>