Histogram with colored tail




This post describes how to build a histogram with colored tail. It follows the previous basic histogram. An if-else statement is made when the color argument is called. Annotation are also provided. See many other examples in the histogram section of the gallery.


Histogram section

Steps:

  • This plot follows the basic histogram post.

  • To change the color, simply pass an if-else statement when setting the fill argument of the rect.

  • Note that the annotation is easy to add as well, simply appending a line and a text.
<!DOCTYPE html>
<meta charset="utf-8">

<!-- Load d3.js -->
<script src="https://d3js.org/d3.v4.js"></script>

<!-- Create a div where the graph will take place -->
<div id="my_dataviz"></div>


<script>

// set the dimensions and margins of the graph
var margin = {top: 10, right: 30, bottom: 30, left: 40},
    width = 460 - margin.left - margin.right,
    height = 400 - margin.top - margin.bottom;

// append the svg object to the body of the page
var svg = d3.select("#my_dataviz")
  .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 + ")");

// get the data
d3.csv("https://raw.githubusercontent.com/holtzy/data_to_viz/master/Example_dataset/1_OneNum.csv", function(data) {

  // X axis: scale and draw:
  var x = d3.scaleLinear()
      .domain([0, 1000])     // can use this instead of 1000 to have the max of data: d3.max(data, function(d) { return +d.price })
      .range([0, width]);
  svg.append("g")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));

  // set the parameters for the histogram
  var histogram = d3.histogram()
      .value(function(d) { return d.price; })   // I need to give the vector of value
      .domain(x.domain())  // then the domain of the graphic
      .thresholds(x.ticks(70)); // then the numbers of bins

  // And apply this function to data to get the bins
  var bins = histogram(data);

  // Y axis: scale and draw:
  var y = d3.scaleLinear()
      .range([height, 0]);
      y.domain([0, d3.max(bins, function(d) { return d.length; })]);   // d3.hist has to be called before the Y axis obviously
  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 x(d.x1) - x(d.x0) -1 ; })
        .attr("height", function(d) { return height - y(d.length); })
        .style("fill", function(d){ if(d.x0<140){return "orange"} else {return "#69b3a2"}})

  // Append a vertical line to highlight the separation
  svg
    .append("line")
      .attr("x1", x(140) )
      .attr("x2", x(140) )
      .attr("y1", y(0))
      .attr("y2", y(1600))
      .attr("stroke", "grey")
      .attr("stroke-dasharray", "4")
  svg
    .append("text")
    .attr("x", x(190))
    .attr("y", y(1400))
    .text("threshold: 140")
    .style("font-size", "15px")

});
</script>

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