Exercise

Heat maps

Since heat maps encode color on a continuous scale, they are difficult to accurately decode, a topic we discussed in the first course. Hence, heat maps are most useful if you have a small number of boxes and/or a clear pattern that allows you to overcome decoding difficulties.

To produce them, map two categorical variables onto the x and y aesthetics, along with a continuous variable onto fill. The geom_tile() layer adds the boxes.

We'll produce the heat map we saw in the video (in the viewer) with the built-in barley dataset. The barley dataset is in the lattice package and has already been loaded for you. Use str() to explore the structure.

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Using barley, plot variety versus year, filled by yield.
Add a geom_tile() layer.