英文:
Get X-coordinates for bars in chart.js 4
问题
I use Chart.js v4.2.1
<html>
<head>
<meta charset="utf-8" />
<title>Bar chart</title>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/chart.js"></script>
</head>
<body>
<div>
<canvas id="barchart"></canvas>
</div>
</body>
<script type="text/javascript">
var canvas = document.getElementById('barchart');
var chart = new Chart(canvas,
{
type: 'bar',
data:
{
labels: ["Audi", "VW", "KIA"],
datasets:
[
{
label: "Cars",
backgroundColor: ["#3e95cd", "#8e5ea2", "#3cba9f"],
data: [2601, 4769, 602],
},
],
},
});
</script>
</html>
To get number of bars I execute chart.data.datasets[0].data.length and get 3.
To get the Y-value for the first bar I do chart.data.datasets[0].data[0] and get 2601.
How do I get the X-values (X-coordinates) for the bars?
(I am not interested in using any plugin).
Added:
Here is a sample where chart.scales.x is defined but chart.scales.y is not.
This happen when I add yAxisID which I need in my complete work.
<html>
<head>
<meta charset="utf-8" />
<title>Bar chart</title>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/chart.js"></script>
</head>
<body>
<div>
<canvas id="barchart"></canvas>
<div id="debug"></div>
</div>
<script type="text/javascript">
var canvas = document.getElementById('barchart');
var chart = new Chart(canvas,
{
type: 'bar',
data:
{
labels: ["Audi", "VW", "KIA"],
datasets:
[
{
label: "Cars",
backgroundColor: ["#3e95cd", "#8e5ea2", "#3cba9f"],
data: [2601, 4769, 602],
yAxisID: "cars",
},
],
},
options:
{
scales:
{
cars:
{
position: "left",
ticks:
{
color: "red",
},
grid:
{
display: true,
},
},
},
},
});
var dataSets = chart.data.datasets;
var xPos = chart.scales.x.getPixelForValue(dataSets[0].data[0]);
try
{
var yPos = chart.scales.cars.getPixelForValue(dataSets[0].data[0]); // --> here y is undefined
document.getElementById("debug").innerHTML = "xPos=" + xPos + ", yPos=" + yPos;
}
catch(e)
{
document.getElementById("debug").innerHTML = "xPos=" + xPos + "<br>" + e;
}
</script>
</body>
</html>
英文:
I use Chart.js v4.2.1
<html>
<head>
<meta charset="utf-8" />
<title>Bar chart</title>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/chart.js"></script>
</head>
<body>
<div>
<canvas id="barchart"></canvas>
</div>
</body>
<script type="text/javascript">
var canvas = document.getElementById('barchart');
var chart = new Chart(canvas,
{
type: 'bar',
data:
{
labels: ["Audi", "VW", "KIA"],
datasets:
[
{
label: "Cars",
backgroundColor: ["#3e95cd", "#8e5ea2", "#3cba9f"],
data: [2601, 4769, 602],
},
],
},
});
</script>
</html>
To get number of bars I execute chart.data.datasets[0].data.length and get 3.
To get the Y-value for the first bar I do chart.data.datasets[0].data[0] and get 2601.
How do I get the X-values (X-coordinates) for the bars?
(I am not interested in using any plugin).
Added:
Here is a sample where chart.scales.x is defined but chart.scales.y is not.
This happen when I add yAxisID which I need in my complete work.
<html>
<head>
<meta charset="utf-8" />
<title>Bar chart</title>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/chart.js"></script>
</head>
<body>
<div>
<canvas id="barchart"></canvas>
<div id="debug"></div>
</div>
<script type="text/javascript">
var canvas = document.getElementById('barchart');
var chart = new Chart(canvas,
{
type: 'bar',
data:
{
labels: ["Audi", "VW", "KIA"],
datasets:
[
{
label: "Cars",
backgroundColor: ["#3e95cd", "#8e5ea2", "#3cba9f"],
data: [2601, 4769, 602],
yAxisID: "cars",
},
],
},
options:
{
scales:
{
cars:
{
position: "left",
ticks:
{
color: "red",
},
grid:
{
display: true,
},
},
},
},
});
var dataSets = chart.data.datasets;
var xPos = chart.scales.x.getPixelForValue(dataSets[0].data[0]);
try
{
var yPos = chart.scales.cars.getPixelForValue(dataSets[0].data[0]); // --> here y is undefined
document.getElementById("debug").innerHTML = "xPos=" + xPos + ", yPos=" + yPos;
}
catch(e)
{
document.getElementById("debug").innerHTML = "xPos=" + xPos + "<br>" + e;
}
</script>
</body>
</html>
答案1
得分: 3
你可以使用以下代码: chartInstance.scales.x.getPixelForValue(chart instance.data.labels[labelIndex]
英文:
You can use the following code: chartInstance.scales.x.getPixelForValue(chart instance.data.labels[labelIndex]
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