Dygraph - how can we update chart by sending 1 set of data point, rather than the entire data series

Question

I would like to update the live data by sending 1 set of data point rather than sending whole data series array and old value should get auto deleted.

Answer 1

This can be done starting from sample of the Gallery Dynamic Update

Calling updateOptions after updating the data series.

Here a snipnet showing how to append a new data and delete the oldest one :

var data = [];
var t = new Date();
for (var i = 10; i >= 0; i--) {
    var x = new Date(t.getTime() - i * 1000);
    data.push([x, Math.random()]);
}

var g = new Dygraph(document.getElementById("graph"), data, {height:200});

window.setInterval(function() {
        var x = new Date(); 
        var y = Math.random();
        data.shift();
        data.push([x, y]);
        g.updateOptions( { 'file': data } );
      }, 1000);

<script src="https://cdnjs.cloudflare.com/ajax/libs/dygraph/1.1.1/dygraph-combined.js"></script>
<div id="graph" />