Drawing a mixed stacked horizontal bar/line in chartjs

Question

I've looked at the docs/examples for chartjs, but does anyone know a way to do the following?

• Create bars where the width (x-axis) is variable but the height is always full (aka the entire y-axis)?
• There can be x number of those bars in a chart
• Create a line that spans all the way across the x axis but can change it's y-axis (aka not a straight line, but a curvy one).

I have a crude drawing here where the yellow is the bars and the black is the line

• https://ibb.co/3M95JGv

I kinda got the first part down using stacked bars and swapping the axis, but the y-axis (the bars height) is only set to 1. That's a problem when trying to draw a curved line in mixed mode since there is only one y-axis point (instead of many y-axis points):

• https://codepen.io/anon/pen/wVqONp

Here's another attempt that has multiple y-axis points, but I cannot control the bar widths:

• https://codepen.io/uglyhobbitfeet/pen/YzzLmNE?editors=1010

If anyone can help (or at least tell me if I'm going in the right direction), it would be greatly appreciated!

Please see code in the jsfiddle link

Answer 1

Hmh, that's difficult... The only solution I would have is to create a bar chart with very many very small bars.

I made a JSBin with my solution but it's far from perfect, but the only way to achieve it in chart.js. I didn't test the performance as I don't know your data, but this will be very important and the biggest problem.

Right now only one rectangle is possible, but it's not difficult to improve it to multiple rectangles.

Here's all my code, same as JSBin:

var chartData = {
  datasets: [{
    type: 'line',
    label: 'Dataset 1',
    borderColor: 'blue',
    borderWidth: 2,
    fill: false,
    data: []
  }, {
    type: 'bar',
    label: 'Dataset 2',
    backgroundColor: 'red',
    data: [],
  }]
};

var newData0 = []
var newData1 = []
var labels = []
var counter = 50

// Rectangle between two random Integers
var rectangleBetween = [Math.round(Math.random()*counter), Math.round(Math.random()*counter)]
rectangleBetween.sort(function(a, b){return a - b})

for (var i = 0; i < counter; i++) {
  labels.push(i)

  // Data for Dataset 1 (line):
  var newObj0 = {}
  newObj0.x = i
  // 50/50 chance of data
  if (Math.random()<0.5) {
    newObj0.y = Math.round(Math.random()*100)
  } else {
    newObj0.y = null
  }
  newData0.push(newObj0)

  // Data for Dataset 2 (bar):
  var newObj1 = {}
  if (i >= rectangleBetween[0] && i <= rectangleBetween[1]) {
    newObj1.x = i
    newObj1.y = 100
  } else {
    newObj1.x = i
    newObj1.y = 0
  }  
  newData1.push(newObj1)
}

chartData.datasets[0].data = newData0
chartData.datasets[1].data = newData1
chartData.labels = labels


var ctx = document.getElementById('chart').getContext('2d');
myMixedChart = new Chart(ctx, {
  type: 'bar',
  data: chartData,
  options: {
    responsive: true,
    spanGaps: true,
    title: {
      display: true,
      text: 'Chart.js Combo Bar Line Chart'
    },
    tooltips: {
      mode: 'index',
      intersect: true
    },
    scales: {
      xAxes: [{
        //barThickness: 80, // number (pixels) or 'flex'
        //maxBarThickness: 100, // number (pixels)
        barPercentage: 1.0,
        categoryPercentage: 1.0,
        gridLines: {
          display: false
        }
      }]
    }
  }
});

Answer 2

It looks like this is the best solution:

https://codepen.io/kurkle/pen/ExxdyXQ

var ctx = document.getElementById("chart").getContext("2d");
var chart = new Chart(ctx, {
  type: "horizontalBar",
  data: {
    labels: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
    datasets: [
      {
        label: "Bar1",
        data: [[2.5, 5.7]],
      },
      {
        label: "Bar2",
        data: [[6, 8]],
      },
      {
        label: "Bar3",
        data: [[9,10]],
      },
      {
        label: "Line",
        type: "line",
        backgroundColor: "rgb(75, 192, 192, 0.5)",
        borderColor: "rgb(75, 192, 192)",
        fill: false,
        tension: 0,
        data: [11, 10, 9, 8, 7, 6, 5, 4, 3, 2],
        yAxisID: "line"
      }
    ]
  },
  options: {
    datasets: {
      horizontalBar: {
        backgroundColor: "rgb(255, 99, 132, 0.5)",
        borderColor: "rgb(255, 99, 132)",
        borderWidth: 1,
        barPercentage: 1,
        categoryPercentage: 1,
        yAxisID: "bar"
      }
    },
    scales: {
      yAxes: [
        {
          id: "bar",
          type: 'category',
          stacked: true,
          labels: ['bar'],
          offset: true
        },
        {
          id: "line",
          position: 'right',
          ticks: {
            min: 0,
            stepSize: 1
          }
        }
      ]
    }
  }
});

Credit to the original author of this code (Jukka Kurkela aka kurkle). He answered this on the chart.js GitHub issues page.