javascript-d3How do I create a boxplot using d3.js?

To create a boxplot using d3.js, you will need to include the d3.js library in your HTML page. The following code block shows how you can include the d3 library in your HTML page:

<script src="https://d3js.org/d3.v5.min.js"></script>

Once you have included the d3 library, you will need to create a data array to store the data for the boxplot. The following code block shows how you can create a data array with sample data:

var data = [
  [1, 2, 3, 4, 5],
  [2, 4, 6, 8, 10],
  [3, 6, 9, 12, 15]
];

You will then need to create an SVG element to hold the boxplot. The following code block shows how you can create an SVG element:

var svg = d3.select("body")
  .append("svg")
  .attr("width", 500)
  .attr("height", 500);

Once you have the SVG element, you will need to create a boxplot using the data array. The following code block shows how you can create a boxplot using the data array:

var boxplot = svg.selectAll(".box")
  .data(data)
  .enter().append("g")
  .attr("class", "box")
  .attr("transform", function(d, i) { return "translate(" + (i * 50 + 10) + ", 10)"; });

boxplot.append("rect")
  .attr("class", "box")
  .attr("x", 0)
  .attr("y", function(d) { return d3.quantile(d, 0.25); })
  .attr("height", function(d) { return d3.quantile(d, 0.75) - d3.quantile(d, 0.25); })
  .attr("width", 30);

boxplot.append("line")
  .attr("class", "median")
  .attr("x1", 0)
  .attr("x2", 30)
  .attr("y1", function(d) { return d3.quantile(d, 0.5); })
  .attr("y2", function(d) { return d3.quantile(d, 0.5); });

The above code will create a boxplot with three boxes, one for each data array. The boxes will have rectangles representing the interquartile range, and lines representing the median.

Code explanation

**

• d3.select("body"): selects the body element in the HTML page.
• .append("svg"): creates an SVG element in the body element.
• .attr("width", 500): sets the width of the SVG element to 500 pixels.
• .attr("height", 500): sets the height of the SVG element to 500 pixels.
• .selectAll(".box"): selects all elements with class “box” in the SVG element.
• .data(data): binds the data array to the selected elements.
• .enter().append("g"): creates a group element for each element in the data array.
• .attr("class", "box"): sets the class of the group element to “box”.
• .attr("transform", function(d, i) { return "translate(" + (i * 50 + 10) + ", 10)"; }): sets the transform of the group element to translate the group element by an amount equal to the index of the element multiplied by 50 plus 10.
• .append("rect"): creates a rectangle element in the group element.
• .attr("class", "box"): sets the class of the rectangle element to “box”.
• .attr("x", 0): sets the x coordinate of the rectangle element to 0.
• .attr("y", function(d) { return d3.quantile(d, 0.25); }): sets the y coordinate of the rectangle element to the lower quartile of the data array.
• .attr("height", function(d) { return d3.quantile(d, 0.75) - d3.quantile(d, 0.25); }): sets the height of the rectangle element to the difference between the upper quartile and the lower quartile of the data array.
• .attr("width", 30): sets the width of the rectangle element to 30 pixels.
• .append("line"): creates a line element in the group element.
• .attr("class", "median"): sets the class of the line element to “median”.
• .attr("x1", 0): sets the x coordinate of the start point of the line element to 0.
• .attr("x2", 30): sets the x coordinate of the end point of the line element to 30.
• .attr("y1", function(d) { return d3.quantile(d, 0.5); }): sets the y coordinate of the start point of the line element to the median of the data array.
• .attr("y2", function(d) { return d3.quantile(d, 0.5); }): sets the y coordinate of the end point of the line element to the median of the data array.

## Helpful links

• d3.js Documentation
• d3.js Boxplot Tutorial

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