[Solved]-ChartJS: datalabels: show percentage value in Pie piece-Chart.js

if you use nodejs: follow the steps:

1. npm install chartjs-plugin-datalabels
2. import ChartDataLabels from 'chartjs-plugin-datalabels';
3. Chart.register(...registerables, ChartDataLabels);
4. copy the code from the over comments...

https://chartjs-plugin-datalabels.netlify.app/guide/#table-of-contents

As some people mentioned, context.dataset._meta[0].total seem to have been removed in chart.js version 3 and above and didn't work anymore. Instead, I used context.chart.getDatasetMeta(0).total and it worked for me - it shows percentage values in pie chart and value gets updated based on the filtered total when the legends are clicked.

      options:{ 
        plugins:{         
          datalabels: {
            color: 'white',
            formatter: function(value, context) {                  
              return Math.round(value/context.chart.getDatasetMeta(0).total * 100) + "%" ;
            }
          }
        }
      }

I am using ChartJS v3.7.0 and chartjs-plugin-datalabels v2.0.0 and this answer:

https://stackoverflow.com/a/59403435/6830478

does not really work for me, while I just wanted to keep the percentages up to date, also when hiding elements. It seems that ctx.dataset._meta is not available anymore. I came up with some ugly monkey patch:

formatter: function(value, context) {
    var hiddens = context.chart._hiddenIndices;
    var total = 0;
    var datapoints = context.dataset.data;
    datapoints.forEach((val, i) => {
        if (hiddens[i] != undefined) {
            if (!hiddens[i]) {
                total += val;
            }
        } else {
            total += val;
        }
    });
    var percentage = (value / total * 100).toFixed(2) + '%';
    var out = context.chart.data.labels[context.dataIndex] + '\n' + percentage;
    return out;
}

Hopw this might help anybody. Cheers.

This is update for chart.js >= 3.x and chartjs-plugin-datalabels >= 2.x

chartjs-plugin-datalabels plugin no longer registers itself automatically (docs)

You have to do it manually

Register plugin for all charts

Chart.register(ChartDataLabels)

or only to specific charts

var chart = new Chart(ctx, {
  plugins: [ChartDataLabels],
  options: {
    // ...
  }
})

And here's the code below to render the pie chart

var data = [{
  data: [50, 55, 60, 33],
  backgroundColor: [
    "#4b77a9",
    "#5f255f",
    "#d21243",
    "#B27200"
  ],
  borderColor: "#fff"
}];

var options = {
  tooltips: {
    enabled: false
  },
  plugins: {
    datalabels: {
      formatter: (value, ctx) => {
        const datapoints = ctx.chart.data.datasets[0].data
         const total = datapoints.reduce((total, datapoint) => total + datapoint, 0)
        const percentage = value / total * 100
        return percentage.toFixed(2) + "%";
      },
      color: '#fff',
    }
  }
};

var ctx = document.getElementById("pie-chart").getContext('2d');
var myChart = new Chart(ctx, {
  type: 'pie',
  data: {
  labels: ['India', 'China', 'US', 'Canada'],
    datasets: data
  },
  options: options,
  plugins: [ChartDataLabels],
});

  <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.6.2/chart.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/chartjs-plugin-datalabels/2.0.0/chartjs-plugin-datalabels.min.js"></script>
  <style>
.container {
width: 40%;
margin: 5px auto;
}
  </style>
  <div class="container">
<canvas id="pie-chart"></canvas>
  </div>

You could use the tooltip with an Array reducer to perform the percentage calculation and display it.

  tooltips: {
    callbacks: {
      label: function (tooltipItem, data) {
        try {
          let label = ' ' + data.labels[tooltipItem.index] || '';

          if (label) {
            label += ': ';
          }

          const sum = data.datasets[0].data.reduce((accumulator, curValue) => {
            return accumulator + curValue;
          });
          const value = data.datasets[tooltipItem.datasetIndex].data[tooltipItem.index];

          label += Number((value / sum) * 100).toFixed(2) + '%';
          return label;
        } catch (error) {
          console.log(error);
        }
      }
    }
  }

The problem is how you're calculating sum. See below.

Fiddle

 var data = [{
   data: [50, 55, 60, 33],
   labels: ["India", "China", "US", "Canada"],
   backgroundColor: [
     "#4b77a9",
     "#5f255f",
     "#d21243",
     "#B27200"
   ],
   borderColor: "#fff"
 }];

 var options = {
   tooltips: {
     enabled: false
   },
   plugins: {
     datalabels: {
       formatter: (value, ctx) => {

         let datasets = ctx.chart.data.datasets;

         if (datasets.indexOf(ctx.dataset) === datasets.length - 1) {
           let sum = datasets[0].data.reduce((a, b) => a + b, 0);
           let percentage = Math.round((value / sum) * 100) + '%';
           return percentage;
         } else {
           return percentage;
         }
       },
       color: '#fff',
     }
   }
 };


 var ctx = document.getElementById("pie-chart").getContext('2d');
 var myChart = new Chart(ctx, {
   type: 'pie',
   data: {
     datasets: data
   },
   options: options
 });

I like to add a little in accepted answer, ctx.chart.data.datasets[0].data always gives you entire data even if you filter out some data by clicking on legend, means you will always get same percentage for a country even if you filter out some countries.

I have used context.dataset._meta[0].total to get the filtered total.

Here is the working snippet:

var data = [{
  data: [50, 55, 60, 33],
  backgroundColor: [
    "#4b77a9",
    "#5f255f",
    "#d21243",
    "#B27200"
  ],
  borderColor: "#fff"
}];

var options = {
  tooltips: {
    enabled: true
  },
  plugins: {
    datalabels: {
      formatter: (value, ctx) => {

        let sum = ctx.dataset._meta[0].total;
        let percentage = (value * 100 / sum).toFixed(2) + "%";
        return percentage;


      },
      color: '#fff',
    }
  }
};


var ctx = document.getElementById("pie-chart").getContext('2d');
var myChart = new Chart(ctx, {
  type: 'pie',
  data: {
  labels: ['India', 'China', 'US', 'Canada'],
    datasets: data
  },
  options: options
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chartjs-plugin-datalabels@0.7.0"></script>
<canvas id="pie-chart"></canvas>