4đź‘Ť
Ok let’s put together a minimal reproducible example first (in the question, make sure to have code that someone can either click “run code snippet” here or open a link to a codePen / code Sandbox etc. – you should give the dummy data to allow others to get started right away with an example just like you have it in your screenshot etc.):
var ctx = document.getElementById("overAllScore").getContext('2d');
var totalScoreData = [60,30,50,75,45,41]; // Add data values to array
var averageData = [61,45,55,70,46,52] // Add data values to array
var labels = ["A"," Q", "C","C","A","p"]; // Add labels to array
function colorGenerator() {
return totalScoreData.map((child,index) => {
if (child >= averageData[index]){
return 'rgba(5, 250, 10, 0.2)'
} else {
return 'rgba(255, 99, 132, 0.2)'
}
})
}
var overAllScore = new Chart(ctx, {
type: 'bar',
data: {
labels: labels,
datasets: [{
label: 'Scores', // Name the series
data: totalScoreData,
backgroundColor: colorGenerator, //set the colors with a function
borderWidth: 1
},
{
label: 'AvgScore',
data: averageData,
backgroundColor: '#f443368c',
borderColor: '#f443368c',
borderWidth: 1, // Specify bar border width
type: 'line',
fill: false
}]
},
options: {
responsive: true, // Instruct chart js to respond nicely.
maintainAspectRatio: false,
scales: {
yAxes: [{
display: true,
ticks: {
beginAtZero: true,
steps: 10,
max: 100
}
}]
}
}
});
///from chart.js docs:
/*
var chartData = {
labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
datasets: [{
type: 'line',
label: 'Dataset 1',
borderColor: window.chartColors.blue,
borderWidth: 2,
fill: false,
data: [
1,2,3,4,5,6,7
]
}, {
type: 'bar',
label: 'Dataset 2',
backgroundColor: window.chartColors.red,
data: [
2,3,4,5,6,7,8
],
borderColor: 'white',
borderWidth: 2
}]
};
window.onload = function() {
var ctx = document.getElementById('canvas').getContext('2d');
window.myMixedChart = new Chart(ctx, {
type: 'bar',
data: chartData,
options: {
responsive: true,
title: {
display: true,
text: 'Chart.js Combo Bar Line Chart'
},
tooltips: {
mode: 'index',
intersect: true
}
}
});
};
*/<canvas id="overAllScore" style="display: block; width: 765px; height: 382px;" width="765" height="382" class="chartjs-render-monitor"></canvas>
<script src="https://cdn.jsdelivr.net/npm/chart.js@2.8.0"></script>Next, we can figure out a way to change the color of the bar based on its value and the average value.
The result is this:
And to achieve this we needed to do the following:
Firstly, set up the two data arrays:
var totalScoreData = [60,30,50,75,45,41];
var averageData = [61,45,55,70,46,52]
Then modify the new Chart constructor:
var overAllScore = new Chart(ctx, {
type: 'bar',
data: {
labels: labels,
datasets: [{
label: 'Scores', // Name the series
data: totalScoreData,
backgroundColor: colorGenerator, //set the colors with a function
borderWidth: 1
},
{
label: 'AvgScore',
data: averageData,
backgroundColor: '#f443368c',
borderColor: '#f443368c',
borderWidth: 1, // Specify bar border width
type: 'line',
fill: false
}]
}, ...
The key line to notice here is backgroundColor: colorGenerator, for the scores dataset. This means assign the colors based on a function.
This function looks like this:
function colorGenerator() {
return totalScoreData.map((child,index) => {
if (child >= averageData[index]){
return 'rgba(5, 250, 10, 0.2)' //green
} else {
return 'rgba(255, 99, 132, 0.2)' //red
}
})
}
What it does is take the totalScoreData array and map over it, wherever it is above the corresponding average data at the same index – averageData[index] then return a green color, otherwise return the red color.
That’s it 🙂