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javascriptchartsinterpolationdygraphs

Is it possible to show interpolated data using dygraphs?

I have been working for the last months with dygraphs. It is a incredible library and I have got great results but I´m having some problems to find the way of interpolating data from different signals to be shown in the same chart.

The data I received from different sensors have not the same timestamp for the different samples, so for the most of the points of the x axe timestamps I have only the value of one signal. The chart is plotted perfectly, but I would like to see the interpolated value of the rest of the signals in that x point I am pointing over. Below I have the chart I get.

enter image description here

Reading on the dygraph documentation I have seen that when you have independent series, it is possible to see at least the value "undefined" for the signals without data in that point of the x axe.

The csv I use to plot the data is shown below. It has the same structure indicated in the dygraph documentation but I don´t get this undefined label neither.

TIME,LH_Fuel_Qty,L_Left_Sensor_NP 1488801288048,,1.4411650490795007 1488801288064,0.478965502446834, 1488801288133,,0.6372882768113235 1488801288139,1.131315227899919, 1488801288190,1.847605177130475, 1488801288207,,0.49655791428536067 1488801288258,0.45488168748987334, 1488801288288,,1.3756073145270766 1488801288322,0.5636921255908185, 1488801288358,,1.1193344122758362

Thanks in advance.

Solution

  • This is an approach that does not add any data to your csv data and still provides interpolated values for all the columns as you move your mouse around. It adds a listener to the mousemove event within dygraph and interpolates the closest points for all of the data. At the moment I have simply shown it in an extra DIV that is after the graph but you can display it however you like:

    function findNextValueIndex(data, column, start) {
  var rows = data.length;

  for (var i = start; i < rows; i++) {
    if (data[i][column] != null) return (i);
  }
  return (-1);
}

function findPrevValueIndex(data, column, start) {

  for (var i = start; i >= 0; i--) {
    if (data[i][column] != null) return (i);
  }
  return (-1);
}

function interpolate(t0, t1, tmid, v0, v1) {
  return (v0 + (tmid - t0) / (t1 - t0) * (v1 - v0));
}

function showValues(headers, colors, vals) {
  var el = document.getElementById("info");
  var str = "";
  for (j = 1; j < headers.length; j++) {
    str += '<p style="color:' + colors[j] + '";>' + headers[j] + ": " + vals[j] + "</p>";
  }
  el.innerHTML = str;
  document.getElementById("hiddenDiv").style.display = "none";
}

function movecustom(event, dygraph, point) {
  var time = dygraph.lastx_;
  var row = dygraph.lastRow_;
  var vals = [];
  var headers = [];
  var colors = [];
  var cols = dygraph.rawData_[0].length;
  
  // draw a line on the chart showing the selected location
  var canvas = dygraph.canvas_;
  var ctx = canvas.getContext("2d");

  ctx.beginPath();
  ctx.lineWidth = 1;
  ctx.strokeStyle = "rgba(0,200,200,0.1)";
  ctx.moveTo( dygraph.selPoints_[0].canvasx, 0);
  ctx.lineTo( dygraph.selPoints_[0].canvasx, 1000);
  ctx.stroke();
  
  
  for (var j = 1; j < cols; j++) {
    colors[j] = dygraph.colors_[j - 1];
    if (dygraph.rawData_[row][j] == null) {
      var prev = findPrevValueIndex(dygraph.rawData_, j, row - 1);
      var next = findNextValueIndex(dygraph.rawData_, j, row + 1);
      if (prev < 0)
        vals[j] = dygraph.rawData_[next][j];
      else if (next < 0)
        vals[j] = dygraph.rawData_[prev][j];
      else {
        vals[j] = interpolate(dygraph.rawData_[prev][0], dygraph.rawData_[next][0], time, dygraph.rawData_[prev][j], dygraph.rawData_[next][j]);
      }
    } else {
      vals[j] = dygraph.rawData_[row][j];
    }
  }

  headers = Object.keys(dygraph.setIndexByName_);

  showValues(headers, colors, vals);
}

window.onload = function() {

  new Dygraph(
    document.getElementById('graph'), document.getElementById('csvdata').innerHTML, {
      connectSeparatedPoints: true,
      drawPoints: true,
      labelsDiv: "hiddenDiv",
      interactionModel: {
        'mousemove': movecustom
      }
    }
  );
}
    <script src="https://cdnjs.cloudflare.com/ajax/libs/dygraph/2.0.0/dygraph.js"></script>

<div id="graph" style="height:120px;"></div>

<div id="info"></div>
<div id="hiddenDiv" style="display:none"></div>

<pre id="csvdata" style="display:none">
TIME,LH_Fuel_Qty,L_Left_Sensor_NP
1488801288048,,1.4411650490795007
1488801288064,0.478965502446834,
1488801288133,,0.6372882768113235
1488801288139,1.131315227899919,
1488801288190,1.847605177130475,
1488801288207,,0.49655791428536067
1488801288258,0.45488168748987334,
1488801288288,,1.3756073145270766
1488801288322,0.5636921255908185,
1488801288358,,1.1193344122758362
</pre>