Library for adding a tooltip to a d3 brush.
Adding the tooltip to a d3 brush requires importing the library and providing a bit of css. Below you will find a sample html file and sample style for the label, which allows for it to be positioned alongside the cursor.
<!DOCTYPE html>
<script src="https://cdn.jsdelivr.net/npm/d3@7"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-brush-tooltip@1.0.1"></script>
<link rel="stylesheet" href="css/style.css">
<html>
<body>
<div id="chart-div">
<div id="tooltip" class="tooltip-default"/>
</div>
<script>
// create chart
let width = 600;
let height = 400;
const margin = { top: 10, right: 30, bottom: 30, left: 40 };
width = width - margin.left - margin.right,
height = height - margin.top - margin.bottom;
// append the svg object to the body of the page
var svg = d3.select("#chart-div")
.append("svg")
.attr("width", width + margin.left + margin.right)
.attr("height", height + margin.top + margin.bottom)
.append("g")
.attr("transform",
"translate(" + margin.left + "," + margin.top + ")");
const maxX = 1000;
// add x axis
const x = d3.scaleLinear()
.domain([0, maxX])
.range([0, width]);
svg.append("g")
.attr("transform", "translate(0," + height + ")")
.call(d3.axisBottom(x));
// generate random data
const data = [];
for (let i = 0; i < 1000; i++) {
data.push(Math.random() * maxX);
}
// create bins
const bin = d3.bin()
.domain(x.domain())
.thresholds(x.ticks(20));
const bins = bin(data);
// add y axis
const y = d3.scaleLinear()
.domain([0, d3.max(bins, function (d) { return d.length; })])
.range([height, 0]);
svg.append("g")
.call(d3.axisLeft(y));
// append the bar rectangles to the svg element
svg.selectAll("rect")
.data(bins)
.enter()
.append("rect")
.attr("x", 1)
.attr("transform", function (d) { return "translate(" + x(d.x0) + "," + y(d.length) + ")"; })
.attr("width", function (d) { return Math.max(0, x(d.x1) - x(d.x0) - 1); })
.attr("height", function (d) { return height - y(d.length); })
.style("fill", "#69b3a2")
// add a brush container to the chart
const brushContainer = svg.append("g");
// create the brush
const brush = d3.brushX().extent([[0, 0], [width, height]]);
brushContainer.call(brush);
// move brush to the initial position
const initialSelection = [x(100), x(200)];
brushContainer.call(brush.move, initialSelection);
const tooltipId = "#tooltip";
// function that takes a selection and provides the count of records within those bounds
function getTooltipText(selection) {
if (selection) {
const min = Math.round(x.invert(selection[0]));
const max = Math.round(x.invert(selection[1]));
const count = data.filter(value => value >= min && value <= max).length;
return `${min} - ${max}: ${count} records`;
} else {
return null;
}
}
// add tooltip to the brush
window.d3BrushTooltip.addTooltipToBrush(tooltipId, brush, brushContainer, (brushEvent) => {
const selection = brushEvent.selection;
return getTooltipText(selection);
}, getTooltipText(initialSelection));
</script>
</body>
</html>.tooltip-default {
opacity: 1;
background-color: white;
border: solid 1px black;
padding: 4px;
border-radius: 4px;
white-space: nowrap;
pointer-events: none;
display: none;
z-index: 2;
user-select: none;
position: fixed;
}