Data shapes

What sort of data is each chart expecting?

Every chart takes the output of group.all(), i.e. an array of {key,value} pairs. However, the interpretation of the key can vary, and some charts take multiple groups.

Bubble chart and bubble overlay

By default, X and Y are driven by the keyAccessor and valueAccessor, respectively. However, these can be overridden to give bubbles some other identity if they change coordinates in response to filters.

Scatter plot and heatmap

The key is an array of X and Y coordinates. This does not allow symbols/cells to change position. (#621, #702).

Sometimes people stick the color in a third element of the array because it's easier to create a custom key than a custom value.