Published
Edited
Jun 24, 2020
Insert cell
md`# Making zoomable and sorted bar chart`
Insert cell
md`Loading D3.js package into the Observable environment:`
Insert cell
d3 = require("d3@5")
Insert cell
md`Defining color, size, and margin attributes of the bar chart:`
Insert cell
color = "steelblue"
Insert cell
height = 500
Insert cell
margin = ({top: 30, right: 0, bottom: 30, left: 40})
Insert cell
md`Loading data:`
Insert cell
data = d3.csvParse(await FileAttachment("data-sc.csv").text(), d3.autoType)
Insert cell
sortedData = data.slice().sort((a, b) => d3.descending(a.Cases, b.Cases))
Insert cell
md`Defining scales and axes:`
Insert cell
x = d3.scaleBand()
.domain(sortedData.map(d => d.County))
.range([margin.left, width - margin.right])
.padding(0.1)
Insert cell
y = d3.scaleLinear()
.domain([0, d3.max(sortedData, d => d.Cases)]).nice()
.range([height - margin.bottom, margin.top])
Insert cell
xAxis = g => g
.attr("transform", `translate(0,${height - margin.bottom})`)
.call(d3.axisBottom(x).tickSizeOuter(0))
Insert cell
yAxis = g => g
.attr("transform", `translate(${margin.left},0)`)
.call(d3.axisLeft(y))
.call(g => g.select(".domain").remove())
Insert cell
md`#Creating zoom interaction function:`
Insert cell
function zoom(svg) {
const extent = [[margin.left, margin.top], [width - margin.right, height - margin.top]];

svg.call(d3.zoom()
.scaleExtent([1, 8])
.translateExtent(extent)
.extent(extent)
.on("zoom", zoomed));

function zoomed() {
x.range([margin.left, width - margin.right].map(d => d3.event.transform.applyX(d)));
svg.selectAll(".bars rect").attr("x", d => x(d.County)).attr("width", x.bandwidth());
svg.selectAll(".x-axis").call(xAxis);
}
}
Insert cell
md`Creating bar chart:`
Insert cell
chart = {
const svg = d3.create("svg")
.attr("viewBox", [0, 0, width, height])
.call(zoom);

svg.append("g")
.attr("class", "bars")
.attr("fill", "steelblue")
.selectAll("rect")
.data(sortedData)
.join("rect")
.attr("x", d => x(d.County))
.attr("y", d => y(d.Cases))
.attr("height", d => y(0) - y(d.Cases))
.attr("width", x.bandwidth());

svg.append("g")
.attr("class", "x-axis")
.call(xAxis);

svg.append("g")
.attr("class", "y-axis")
.call(yAxis);

return svg.node();
}
Insert cell

Purpose-built for displays of data

Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
Learn more