Use condition() as the value of a mark aesthetic to make that aesthetic
depend on whether an element is in a selection: members get
if_true, non-members get if_false. This is the general form of
highlight-on-interaction.
Arguments
- selection
The selection name (a string) that drives the condition.
- if_true
The aesthetic value for selection members — a column expression (data-masked) or a constant.
- if_false
The value for non-members — a constant, or omitted to use the theme's dim appearance.
- empty
Whether an empty selection matches all elements (
TRUE, default).
Details
condition() is recognised where it appears in a mark_*() encoding; calling
it directly is an error. The if_true branch is drawn on a static render and
trains scales exactly as the equivalent plain encoding, so
color = condition("s", g, "grey80") produces the same colour scale and legend
as color = g. With empty = TRUE (the default) an empty selection matches
everything, so a static / initial render shows if_true for all elements and
interaction dims non-members to if_false.