ChartJS: datalabels: show percentage value in Pie piece

问题

I have a piechart with four labels:

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

Using chartjs-plugin-datalabels plugin I wanted to show percentage value in each Pie piece with below code:

formatter: (value, ctx) => {

        let datasets = ctx.chart.data.datasets;

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

I am getting 100% value for all the pie pieces, instead of respective percentages. Here is the JSFiddle (https://jsfiddle.net/kingBethal/a1Lvn4eb/7/)

回答1:

Updated fiddle with 2 decimal precision.

You were not computing the sum, instead storing the current value in sum only for every value.

Here is the working fiddle : https://jsfiddle.net/a1Lvn4eb/55/

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 sum = 0;
                let dataArr = ctx.chart.data.datasets[0].data;
                dataArr.map(data => {
                    sum += data;
                });
                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: {
        datasets: data
    },
    options: options
});

回答2:

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
 });

回答3:

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);
        }
      }
    }
  }

来源：https://stackoverflow.com/questions/52044013/chartjs-datalabels-show-percentage-value-in-pie-piece