Book Image

D3.js Quick Start Guide

By : Matthew Huntington
Book Image

D3.js Quick Start Guide

By: Matthew Huntington

Overview of this book

D3.js is a JavaScript library that allows you to create graphs and data visualizations in the browser with HTML, SVG, and CSS. This book will take you from the basics of D3.js, so that you can create your own interactive visualizations, to creating the most common graphs that you will encounter as a developer, scientist, statistician, or data scientist. The book begins with an overview of SVG, the basis for creating two-dimensional graphics in the browser. Once the reader has a firm understanding of SVG, we will tackle the basics of how to use D3.js to connect data to our SVG elements. We will start with a scatter plot that maps run data to circles on a graph, and expand our scatter plot to make it interactive. You will see how you can easily allow the users of your graph to create, edit, and delete run data by simply dragging and clicking the graph. Next, we will explore creating a bar graph, using external data from a mock API. After that, we will explore animations and motion with a bar graph, and use various physics-based forces to create a force-directed graph. Finally, we will look at how to use GeoJSON data to create a map.
Table of Contents (10 chapters)

Changing the color of the bar based on data

Right now, the bars are black. A linear scale will interpolate between colors, just like a regular number. Add the following to the end of the AJAX callback:

var yDomain = d3.extent(data, function(datum, index){
    return datum.count;
})
var colorScale = d3.scaleLinear();
colorScale.domain(yDomain)
colorScale.range(['#00cc00', 'blue'])
d3.selectAll('rect')
    .attr('fill', function(datum, index){
        return colorScale(datum.count)
    })

Notice that we calculate they Domain using d3.extent so that the real minimum of the data set is used to map #00cc00: