How to make a heat map in R

FlowingData has just posted a nice step-by-step tutorial on how to make a heat-map in R, like this one on attributes of NBA scorers:

If you want to take the concept a step further with time-series data, you can also create calendar heat-maps in R. For example, you can track the level of activity in a forum, or the pace of iPhone app sales.

FlowingData: How to Make a Heatmap – a Quick and Easy Solution