Histogram with D3
A histogram displays the distribution of data over a continuous interval or specific time period. The height of each bar in a histogram indicates the frequency of data points within the interval/bin.
More about: Histogram
Histogram
<!DOCTYPE html>
<meta charset="utf-8">
<!-- Include d3 library -->
<script src="https://d3js.org/d3.v7.min.js"></script>
<!-- Create a container to host the chart -->
<div id="viz_container"></div>
// set the dimensions and margins of the graph
const margin = {top: 60, right: 20, bottom: 50, left: 40};
const width = 450 - margin.left - margin.right;
const height = 350 - margin.top - margin.bottom;
// append the svg object to the body of the page
const svg = d3.select("#viz_container")
.append("svg")
.attr("width", "100%")
.attr("height", "100%")
.attr("viewBox", "0 0 450 350")
.attr("preserveAspectRatio", "xMinYMin")
.append("g")
.attr("transform", `translate(${margin.left}, ${margin.top})`);
// parse the Data
d3.csv("https://raw.githubusercontent.com/GDS-ODSSS/unhcr-dataviz-platform/master/data/distribution/histogram.csv")
.then(function(data){
// X scale and Axis
const xScale = d3.scaleLinear()
.domain([0,100])
.range([0, width]);
svg
.append('g')
.attr("transform", `translate(0, ${height})`)
.call(d3.axisBottom(xScale).tickSize(0).tickPadding(8));
// Y scale and Axis
const yScale = d3.scaleLinear()
.range([height, 0]);
const yAxis = svg.append('g')
// set horizontal grid line
const GridLine = () => d3.axisLeft().scale(yScale);
svg
.append("g")
.attr("class", "grid")
.call(GridLine()
.tickSize(-width,0,0)
.tickFormat("")
.ticks(10)
);
// create a tooltip
const tooltip = d3.select("body")
.append("div")
.attr("class", "tooltip");
// tooltip events
const mouseover = function(d) {
tooltip
.style("opacity", 1)
d3.select(this)
.style("stroke", "#EF4A60")
.style("opacity", .5)
};
const mousemove = function(event,d) {
tooltip
.html(`<b>Number of people</b>: ${d.length}`)
.style("top", event.pageY - 10 + "px")
.style("left", event.pageX + 10 + "px")
};
const mouseleave = function(d) {
tooltip
.style("opacity", 0)
d3.select(this)
.style("stroke", "none")
.style("opacity", 1)
};
// set the parameters for the histogram
const histogram = d3.bin()
.value(d => d.poc_age)
.domain(xScale.domain())
.thresholds(xScale.ticks(50));
// prepare data for bars
const bins = histogram(data)
// Scale the range of the data in the y domain
yScale.domain([0, 20]);
// add the y Axis
yAxis
.call(d3.axisLeft(yScale).tickSize(0).tickPadding(4))
.call(d => d.select(".domain").remove());
// append the bar rectangles to the svg element
svg
.selectAll("rect")
.data(bins)
.join("rect")
.attr("class", "bar")
.attr("x", 1)
.attr("transform", d => `translate(${xScale(d.x0)}, ${yScale(d.length)})`)
.attr("width", d => xScale(d.x1) - xScale(d.x0) - 1)
.attr("height", d => height - yScale(d.length))
.style("fill", "#0072BC")
.on("mouseover", mouseover)
.on("mousemove", mousemove)
.on("mouseleave", mouseleave);
// set title
svg
.append("text")
.attr("class", "chart-title")
.attr("x", -(margin.left)*0.4)
.attr("y", -(margin.top)/1.5)
.attr("text-anchor", "start")
.text("Age distribution | 2020")
// set X axis label
svg
.append("text")
.attr("class", "chart-label")
.attr("x", width/2)
.attr("y", height+margin.bottom/1.7)
.attr("text-anchor", "middle")
.text("Age");
// set Y axis label
svg
.append("text")
.attr("class", "chart-label")
.attr("x", -(margin.left)*0.4)
.attr("y", -(margin.top/5))
.attr("text-anchor", "start")
.text("Number of people")
// set source
svg
.append("text")
.attr("class", "chart-source")
.attr("x", -(margin.left)*0.4)
.attr("y", height + margin.bottom*0.7)
.attr("text-anchor", "start")
.text("Source: UNHCR")
// set copyright
svg
.append("text")
.attr("class", "copyright")
.attr("x", -(margin.left)*0.4)
.attr("y", height + margin.bottom*0.9)
.attr("text-anchor", "start")
.text("©UNHCR, The UN Refugee Agency")
})
