Lecture 6: d3 joins and scales

In this lecture we will see two important parts of d3. The first part is central to how d3 works: it’s the notion of a join. In fact, we already used joins in the last lecture, but today we will spend a long time making sure we understand what is going on with those selectAll().data().enter().append() calls.

The second part is a set of helper libraries to make your function accessors cleaner and more modular. These are D3 scales. They are used extensively inside d3, and so you need to understand how they work, but they are also tremendously convenient to create data visualizations.

D3 joins

Why we need the selectAll().data().enter() pattern
There’s an exit() method, too!
keys for data joins

Reading Material

Basics:

Mike Bostock’s Three Little Circles
- Specifically for keys in joins: Object Constancy
Mike Bostock’s Thinking with joins.
Scott Murray’s “Data” Section from Chapter 5 of his book.

In-depth (optional, but recommended read):

Mike Bostock’s How Selections Work

D3 scales

Linear scales
- What do they do
- More than numbers
- You could have invented them
Log scales
- and others
Interpolators

Reading material

d3 v4 API reference.
Chapter 7 from Scott Murray’s book