CODEWITHSUNDEEP
javascripthtmlchart.js
Benjamin
Benjamin

Reputation: 15

Auto-Remove old Datapoints in Chart.js

I have a Chart for Real time data, which is updated by Javascript.

But if the script runs to long, the data is getting crammed up.

enter image description here

The old Data would have to be shifted to the left side an then be deleted.

Live Demo: https://codepen.io/benni_de/pen/ajGood

Code: 

function reLoad() {

  adddata(Math.random() * 100, Math.random() * 10);
  setTimeout(reLoad, 1000);
}

var canvas = document.getElementById('myChart');
var data = {
  datasets: [{
      label: 'Download',
      borderColor: 'rgb(237, 18, 237)',
      fill: false,
      borderWidth: 3
    },
    {
      label: 'Upload',
      borderColor: 'rgb(0, 115, 255)',
      fill: false,
      borderWidth: 3
    }
  ]
}
var options = {
  scales: {
    yAxes: [{
      type: 'linear',
    }],

    xAxes: [{
      type: 'time',
      ticks: {
        maxTicksLimit: 5,
      },
      time: {
        unit: 'second',
        displayFormats: {
          'second': 'HH:mm:ss',
        },
        tooltipFormat: 'HH:mm:ss',
      }
    }]
  },
  showLines: true
};
var myChart = new Chart.Line(canvas, {
  data: data,
  options: options
});

function adddata(download = NaN, upload = NaN, label = moment()) {
  var datasets = myChart.data.datasets;
  myChart.data.labels.push(label);
  datasets[0].data.push(download);
  datasets[1].data.push(upload);
  myChart.update();
}

reLoad();
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.bundle.min.js"></script>
<canvas id="myChart" width="400px" height="100px"></canvas>

Upvotes: 1

Views: 3216

Answers (1)

Andrew L
Andrew L

Reputation: 5486

To make this work, I added a config var MAX_DATA_SET_LENGTH and then in addData() I check to see if the length of either the upload/download data set is greater than your config.

If the data set is larger than you want, I shift() the data set array (remove the first entry). I also shift/remove the first label too to keep the data accurate.

If you would still like to keep all the data, I would suggest keeping it in a separate array that Chart.js does not use.

Also, I switched the code to use setInterval() instead since it makes more sense here. You want to run addData on an interval instead of once after a timeout (even though you still make it work by setting the timeout multiple times)

var MAX_DATA_SET_LENGTH = 15;

function reLoad() {
  adddata(Math.random() * 100, Math.random() * 10);
}

var canvas = document.getElementById('myChart');
var data = {
  datasets: [{
      label: 'Download',
      borderColor: 'rgb(237, 18, 237)',
      fill: false,
      borderWidth: 3
    },
    {
      label: 'Upload',
      borderColor: 'rgb(0, 115, 255)',
      fill: false,
      borderWidth: 3
    }
  ]
}
var options = {
  scales: {
    yAxes: [{
      type: 'linear',
    }],

    xAxes: [{
      type: 'time',
      ticks: {
        maxTicksLimit: 5,
      },
      time: {
        unit: 'second',
        displayFormats: {
          'second': 'HH:mm:ss',
        },
        tooltipFormat: 'HH:mm:ss',
      }
    }]
  },
  showLines: true
};
var myChart = new Chart.Line(canvas, {
  data: data,
  options: options
});

function adddata(download = NaN, upload = NaN, label = moment()) {
  var datasets = myChart.data.datasets;
  var labels = myChart.data.labels;
  var downloadDataSet = datasets[0].data;
  var uploadDataSet = datasets[1].data;

  var downloadDataLength = downloadDataSet.length;
  var uploadDataLength = uploadDataSet.length;

  // if upload/download's data set has more than MAX_DATA_SET_LENGTH entries, 
  // remove the first one entry and push on a new data entry
  var didRemoveData = false;
  if (downloadDataLength > MAX_DATA_SET_LENGTH) {
    downloadDataSet.shift();
    didRemoveData = true;
  }

  if (uploadDataLength > MAX_DATA_SET_LENGTH) {
    uploadDataSet.shift();
    didRemoveData = true;
  }

  // if either download or upload data was removed, we also need to remove
  // the first label to keep the data from squeezing in.
  if (didRemoveData) {
    labels.shift();
  }

  labels.push(label);
  downloadDataSet.push(download);
  uploadDataSet.push(upload);
  myChart.update();
}


setInterval(reLoad, 1000);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.bundle.min.js"></script>
<canvas id="myChart" width="400px" height="100px"></canvas>

Upvotes: 3

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