8.1 KiB
| title | anchor |
|---|---|
| Bar Chart | bar-chart |
Introduction
A bar chart is a way of showing data as bars.
It is sometimes used to show trend data, and the comparison of multiple data sets side by side.
Example usage
var myBarChart = new Chart(ctx,{
type: 'bar',
data: data,
options: options
});
Data structure
var data = {
labels: ["January", "February", "March", "April", "May", "June", "July"],
datasets: [
{
label: "My First dataset",
// The properties below allow an array to be specified to change the value of the item at the given index
// String or array - the bar color
backgroundColor: "rgba(220,220,220,0.2)",
// String or array - bar stroke color
borderColor: "rgba(220,220,220,1)",
// Number or array - bar border width
borderWidth: 1,
// String or array - fill color when hovered
hoverBackgroundColor: "rgba(220,220,220,0.2)",
// String or array - border color when hovered
hoverBorderColor: "rgba(220,220,220,1)",
// The actual data
data: [65, 59, 80, 81, 56, 55, 40],
// String - If specified, binds the dataset to a certain y-axis. If not specified, the first y-axis is used.
yAxisID: "y-axis-1",
},
{
label: "My Second dataset",
backgroundColor: "rgba(220,220,220,0.2)",
borderColor: "rgba(220,220,220,1)",
borderWidth: 1,
hoverBackgroundColor: "rgba(220,220,220,0.2)",
hoverBorderColor: "rgba(220,220,220,1)",
data: [28, 48, 40, 19, 86, 27, 90]
}
]
};
The bar chart has the a very similar data structure to the line chart, and has an array of datasets, each with colours and an array of data. Again, colours are in CSS format. We have an array of labels too for display. In the example, we are showing the same data as the previous line chart example.
The label key on each dataset is optional, and can be used when generating a scale for the chart.
Chart Options
These are the customisation options specific to Bar charts. These options are merged with the global chart configuration options, and form the options of the chart.
{
// Boolean - if true, bars stack on top of each other
stacked: false,
hover: {
// String - We use a label hover mode since the x axis displays data by the index in the dataset
mode: "label"
},
scales: {
// The bar chart officially supports only 1 x-axis but uses an array to keep the API consistent. Use a scatter chart if you need multiple x axes.
xAxes: [{
// String - type of axis to use. Should not be changed from 'dataset'.
scaleType: "dataset", // scatter should not use a dataset axis
// Boolean - if true, show the scale
display: true,
// String - position of the scale. possible options are "top" and "bottom" for dataset scales
position: "bottom",
// String - id of the axis so that data can bind to it
id: "x-axis-1", // need an ID so datasets can reference the scale
// grid line settings
gridLines: {
// Boolean - if true, show the grid lines
show: true,
// String - color of the grid lines
color: "rgba(0, 0, 0, 0.05)",
// Number - width of the grid lines
lineWidth: 1,
// Boolean - if true draw lines on the chart area
drawOnChartArea: true,
// Boolean - if true draw ticks in the axis area
drawTicks: true,
// Number - width of the grid line for the first index (index 0)
zeroLineWidth: 1,
// String - color of the grid line for the first index
zeroLineColor: "rgba(0,0,0,0.25)",
// Boolean - if true, offset labels from grid lines
offsetGridLines: false,
},
// label settings
labels: {
// Boolean - if true show labels
show: true,
// String - template string for labels
template: "<%=value%>",
// Number - label font size
fontSize: 12,
// String - label font style
fontStyle: "normal",
// String - label font color
fontColor: "#666",
// String - label font family
fontFamily: "Helvetica Neue",
},
}],
yAxes: [{
// String - type of axis. 'linear' is the default but extensions may provide other types such as logarithmic
scaleType: "linear",
// Boolean - if true, show the scale
display: true,
// String - position of axis. Vertical axes can have either "left" or "right"
position: "left",
// ID of the axis for data binding
id: "y-axis-1",
// grid line settings
gridLines: {
// Boolean - if true, show the grid lines
show: true,
// String - color of the grid lines
color: "rgba(0, 0, 0, 0.05)",
// Number - width of the grid lines
lineWidth: 1,
// Boolean - if true draw lines on the chart area
drawOnChartArea: true,
// Boolean - if true draw ticks in the axis area
drawTicks: true,
// Number - width of the grid line representing a numerical value of 0
zeroLineWidth: 1,
// String - color of the grid line representing a numerical value of 0
zeroLineColor: "rgba(0,0,0,0.25)",
},
// Boolean - if true ensures that the scale always has a 0 point
beginAtZero: false,
// Object - if specified, allows the user to override the step generation algorithm.
// Contains the following values
// start: // number to start at
// stepWidth: // size of step
// steps: // number of steps
override: null,
// label settings
labels: {
// Boolean - if true show labels
show: true,
// String - template string for labels
template: "<%=value%>",
// Function - if specified this is passed the tick value, index, and the array of all tick values. Returns a string that is used as the label for that value
userCallback: null,
// Number - label font size
fontSize: 12,
// String - label font style
fontStyle: "normal",
// String - label font color
fontColor: "#666",
// String - label font family
fontFamily: "Helvetica Neue",
},
}],
},
};
You can override these for your Chart instance by passing a second argument into the Bar method as an object with the keys you want to override.
For example, we could have a bar chart without a stroke on each bar by doing the following:
new Chart(ctx).Bar({
data: data,
options: {
barShowStroke: false
}
});
// This will create a chart with all of the default options, merged from the global config,
// and the Bar chart defaults but this particular instance will have `barShowStroke` set to false.
We can also change these defaults values for each Bar type that is created, this object is available at Chart.defaults.Bar.
Prototype methods
.getBarsAtEvent( event )
Calling getBarsAtEvent(event) on your Chart instance passing an argument of an event, or jQuery event, will return the bar elements that are at that the same position of that event.
canvas.onclick = function(evt){
var activeBars = myBarChart.getBarsAtEvent(evt);
// => activeBars is an array of bars on the canvas that are at the same position as the click event.
};
This functionality may be useful for implementing DOM based tooltips, or triggering custom behaviour in your application.
.update( )
Calling update() on your Chart instance will re-render the chart with any updated values, allowing you to edit the value of multiple existing points, then render those in one animated render loop.
myBarChart.datasets[0].bars[2].value = 50;
// Would update the first dataset's value of 'March' to be 50
myBarChart.update();
// Calling update now animates the position of March from 90 to 50.
.addData( valuesArray, label )
Calling addData(valuesArray, label) on your Chart instance passing an array of values for each dataset, along with a label for those bars.
// The values array passed into addData should be one for each dataset in the chart
myBarChart.addData([40, 60], "August");
// The new data will now animate at the end of the chart.
.removeData( )
Calling removeData() on your Chart instance will remove the first value for all datasets on the chart.
myBarChart.removeData();
// The chart will now animate and remove the first bar