This chart shows a histogram of an Irwin–Hall distribution. The data is randomly generated. The values are then binned at regular intervals using D3’s histogram layout. The x-axis uses a linear scale, such that the tick values appear between bars; this provides better indication that each bar represents the count of values between its surrounding tick values.
See also this histogram of a log-normal distribution of time durations.
| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <style> | |
| body { | |
| font: 10px sans-serif; | |
| } | |
| .bar rect { | |
| opacity: 0.5; | |
| shape-rendering: crispEdges; | |
| } | |
| .bar text { | |
| fill: #fff; | |
| } | |
| .axis path, .axis line { | |
| fill: none; | |
| stroke: #000; | |
| shape-rendering: crispEdges; | |
| } | |
| .fit { | |
| fill: none; | |
| stroke-width: 4px; | |
| opacity: 0.5; | |
| } | |
| </style> | |
| <body> | |
| <script src="http://d3js.org/d3.v2.min.js?2.10.0"></script> | |
| <script> | |
| // Generate an Irwin–Hall distribution of 10 random variables. | |
| var values = [{"age":12,"blindness":"No","email":"asdfasd","id":"5124561e543c953d690001da","name":"asdfsdfsd","perception":"No","survey_taken":false,"synesthesia":"No","test_taken":false,"tests":[]},{"age":129,"blindness":"No","email":"lasdkjfass","id":"51243cd8543c952efb00000f","name":"hello","perception":"No","survey_taken":false,"synesthesia":"No","test_taken":false,"tests":[]},{"age":123,"blindness":"No","email":"asdfsdf","id":"512454af543c953d690001b5","name":"asdfsdf","perception":"No","survey_taken":false,"synesthesia":"No","test_taken":true,"tests":[{"attempts":1,"display_word":"Green","id":"512455a2543c953d690001c2","question_num":1,"response_time":2313,"text_color":"black"},{"attempts":1,"display_word":"Red","id":"512455a2543c953d690001c3","question_num":2,"response_time":811,"text_color":"black"},{"attempts":1,"display_word":"Purple","id":"512455a2543c953d690001c4","question_num":3,"response_time":941,"text_color":"black"},{"attempts":1,"display_word":"Brown","id":"512455a2543c953d690001c5","question_num":4,"response_time":956,"text_color":"black"},{"attempts":1,"display_word":"Brown","id":"512455a2543c953d690001c6","question_num":5,"response_time":1611,"text_color":"Purple"},{"attempts":1,"display_word":"Red","id":"512455a2543c953d690001c7","question_num":6,"response_time":1147,"text_color":"Red"},{"attempts":1,"display_word":"Purple","id":"512455a2543c953d690001c8","question_num":7,"response_time":1612,"text_color":"Green"},{"attempts":3,"display_word":"Purple","id":"512455a2543c953d690001c9","question_num":8,"response_time":2063,"text_color":"Brown"},{"attempts":1,"display_word":"Green","id":"512455a2543c953d690001ca","question_num":9,"response_time":1370,"text_color":"Purple"},{"attempts":1,"display_word":"Brown","id":"512455a2543c953d690001cb","question_num":10,"response_time":1478,"text_color":"Brown"},{"attempts":1,"display_word":"Purple","id":"512455a2543c953d690001cc","question_num":11,"response_time":1417,"text_color":"Purple"}]}]; | |
| // A formatter for counts. | |
| var formatCount = d3.format(",.0f"); | |
| var margin = {top: 10, right: 30, bottom: 30, left: 30}, | |
| width = 960 - margin.left - margin.right, | |
| height = 500 - margin.top - margin.bottom; | |
| var x = d3.scale.linear() | |
| .domain([0, 4000]) | |
| .range([0, width]); | |
| var real_tests = d3.merge(values.map(function(e){return e.tests})); | |
| var parts = [real_tests.filter(function(t){ | |
| return t.text_color == "black" | |
| }).map(function(e){return e.response_time}), | |
| real_tests.filter(function(t){ | |
| return t.text_color != "black" | |
| }).map(function(e){return e.response_time})] | |
| // var parts = [d3.range(50).map(d3.random.normal(2500, 400)), d3.range(50).map(d3.random.normal(1900, 200))] | |
| var hist = parts.map(function(e){ | |
| return d3.layout.histogram() | |
| .bins(x.ticks(40))(e) | |
| }) | |
| var ymax = d3.max(hist.map(function(e){ | |
| return d3.max(e, function(d){return d.y}) | |
| })); | |
| var y = d3.scale.linear() | |
| .domain([0, ymax]) | |
| .range([height, 0]); | |
| var xAxis = d3.svg.axis() | |
| .scale(x) | |
| // .tickFormat(d3.format(',.0f ms')) | |
| .orient("bottom"); | |
| var svg = d3.select("body").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 + ")"); | |
| var colors = ["steelblue", "green"] | |
| var histogram = svg.selectAll(".histogram") | |
| .data(hist) | |
| .enter().append("g") | |
| .attr("fill", function(d, i){ return colors[i]} ) | |
| .attr("class", "histogram") | |
| var line = d3.svg.line() | |
| .x(function(d, i) { return x(d[0]); }) | |
| .y(function(d, i) { return y(d[1]); }); | |
| var norm_max = d3.max(parts, function(d){ | |
| var mean = d3.mean(d), stdev = Math.sqrt(d3.mean(d.map(function(e){return Math.pow(e - mean, 2)}))); | |
| var max = 1 / (Math.sqrt(2 * Math.PI) * stdev); | |
| return max | |
| }) | |
| var curve = svg.selectAll(".fit") | |
| .data(parts) | |
| .enter().append("g") | |
| .attr("class", "fit") | |
| .attr("stroke", function(d, i){ return colors[i]} ) | |
| curve.append('svg:path') | |
| .attr("d", function(d){ | |
| return line(d3.range(0, 4000, 10).map(function(x){ | |
| var mean = d3.mean(d), stdev = Math.sqrt(d3.mean(d.map(function(e){return Math.pow(e - mean, 2)}))); | |
| // var max = 1 / (Math.sqrt(2 * Math.PI) * stdev); | |
| var pct_mean = ((1 / ( stdev * Math.sqrt( 2 * Math.PI ))) * Math.exp( - Math.pow(x - mean, 2) / (2 * stdev * stdev))) / norm_max | |
| return [x, pct_mean * ymax] | |
| })) | |
| }) | |
| var bar = histogram.selectAll(".bar") | |
| .data(function(d){ return d }) | |
| .enter().append("g") | |
| .attr("class", "bar") | |
| .attr("transform", function(d) { return "translate(" + x(d.x) + "," + y(d.y) + ")"; }); | |
| bar.append("rect") | |
| .attr("x", 1) | |
| .attr("width", x(hist[0][0].dx) - 1) | |
| .attr("height", function(d) { return height - y(d.y); }) | |
| // bar.append("text") | |
| // .attr("dy", ".75em") | |
| // .attr("y", 6) | |
| // .attr("x", x(hist[0][0].dx) / 2) | |
| // .attr("text-anchor", "middle") | |
| // .text(function(d) { return formatCount(d.y); }); | |
| svg.append("g") | |
| .attr("class", "x axis") | |
| .attr("transform", "translate(0," + height + ")") | |
| .call(xAxis); | |
| </script> |
