Racing Bar Charts and Some data.table Munging

A while ago (and also still a bit) racing bar charts were all the rage on data visualisation forums/twitter. Perhaps one of the real breakout examples is this tweet from the, always excellent, John Burn-Murdochat the Financial Times, looking at the most populous cities in the world since the middle ages: New project: A “Bar Chart Race” animation showing the changing ranks of the 10 biggest cities in the world since 1500.