wrennjb wrennjb - 2 months ago 22
Javascript Question

Chart.js 2.0 doughnut tooltip percentages

I have worked with chart.js 1.0 and had my doughnut chart tooltips displaying percentages based on data divided by dataset, but I'm unable to replicate this with chart 2.0.

I have searched high and low and have not found a working solution. I know that it will go under options but everything I've tried has made the pie dysfunctional at best.

<html>

<head>
<title>Doughnut Chart</title>
<script src="../dist/Chart.bundle.js"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<style>
canvas {
-moz-user-select: none;
-webkit-user-select: none;
-ms-user-select: none;
}
</style>
</head>

<body>
<div id="canvas-holder" style="width:75%">
<canvas id="chart-area" />
</div>
<script>
var randomScalingFactor = function() {
return Math.round(Math.random() * 100);
};
var randomColorFactor = function() {
return Math.round(Math.random() * 255);
};
var randomColor = function(opacity) {
return 'rgba(' + randomColorFactor() + ',' + randomColorFactor() + ',' + randomColorFactor() + ',' + (opacity || '.3') + ')';
};

var config = {
type: 'doughnut',
data: {
datasets: [{
data: [
486.5,
501.5,
139.3,
162,
263.7,
],
backgroundColor: [
"#F7464A",
"#46BFBD",
"#FDB45C",
"#949FB1",
"#4D5360",
],
label: 'Expenditures'
}],
labels: [
"Hospitals: $486.5 billion",
"Physicians & Professional Services: $501.5 billion",
"Long Term Care: $139.3 billion",
"Prescription Drugs: $162 billion",
"Other Expenditures: $263.7 billion"
]
},
options: {
responsive: true,
legend: {
position: 'bottom',
},
title: {
display: false,
text: 'Chart.js Doughnut Chart'
},
animation: {
animateScale: true,
animateRotate: true
}

}
};

window.onload = function() {
var ctx = document.getElementById("chart-area").getContext("2d");
window.myDoughnut = new Chart(ctx, config);{

}
};


</script>
</body>

</html>

Answer

In options you can pass in a tooltips object (more can be read at the chartjs docs)

A field of tooltips, to get the result you want, is a callbacks object with a label field. label will be a function that takes in the tooltip item which you have hovered over and the data which makes up your graph. Just return a string, that you want to go in the tooltip, from this function.

Here is an example of what this can look like

tooltips: {
  callbacks: {
    label: function(tooltipItem, data) {
      //get the concerned dataset
      var dataset = data.datasets[tooltipItem.datasetIndex];
      //calculate the total of this data set
      var total = dataset.data.reduce(function(previousValue, currentValue, currentIndex, array) {
        return previousValue + currentValue;
      });
      //get the current items value
      var currentValue = dataset.data[tooltipItem.index];
      //calculate the precentage based on the total and current item, also this does a rough rounding to give a whole number
      var precentage = Math.floor(((currentValue/total) * 100)+0.5);

      return precentage + "%";
    }
  }
} 

and a full example with the data you provided

fiddle

var randomScalingFactor = function() {
  return Math.round(Math.random() * 100);
};
var randomColorFactor = function() {
  return Math.round(Math.random() * 255);
};
var randomColor = function(opacity) {
  return 'rgba(' + randomColorFactor() + ',' + randomColorFactor() + ',' + randomColorFactor() + ',' + (opacity || '.3') + ')';
};

var config = {
  type: 'doughnut',
  data: {
    datasets: [{
      data: [
        486.5,
        501.5,
        139.3,
        162,
        263.7,
      ],
      backgroundColor: [
        "#F7464A",
        "#46BFBD",
        "#FDB45C",
        "#949FB1",
        "#4D5360",
      ],
      label: 'Expenditures'
    }],
    labels: [
      "Hospitals: $486.5 billion",
      "Physicians & Professional Services: $501.5 billion",
      "Long Term Care: $139.3 billion",
      "Prescription Drugs: $162 billion",
      "Other Expenditures: $263.7 billion"
    ]
  },
  options: {
    responsive: true,
    legend: {
      position: 'bottom',
    },
    title: {
      display: false,
      text: 'Chart.js Doughnut Chart'
    },
    animation: {
      animateScale: true,
      animateRotate: true
    },
    tooltips: {
      callbacks: {
        label: function(tooltipItem, data) {
        	var dataset = data.datasets[tooltipItem.datasetIndex];
          var total = dataset.data.reduce(function(previousValue, currentValue, currentIndex, array) {
            return previousValue + currentValue;
          });
          var currentValue = dataset.data[tooltipItem.index];
          var precentage = Math.floor(((currentValue/total) * 100)+0.5);         
          return precentage + "%";
        }
      }
    }
  }
};


var ctx = document.getElementById("chart-area").getContext("2d");
window.myDoughnut = new Chart(ctx, config); {

}
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.1.3/Chart.bundle.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="canvas-holder" style="width:75%">
  <canvas id="chart-area" />
</div>