Link the paired observations with a line
link_line(..., .element = NULL)<dyn-dots> A list of formulas, where each side
of the formula should be an integer or character index of the original
data, or a range_link() object defining the linked observations. Use
NULL to indicate no link on that side. You can also combine these by
wrapping them into a single list(). If only the left-hand side of the
formula exists, you can input it directly. For integer indices, wrap them
with I() to use the ordering from the layout. You can also use
waiver() to inherit values from the other group.
A element_line() object.
Vectorized fields will be recycled to match the total number of groups, or
you can wrap the element with I() to recycle to match the drawing
groups. The drawing groups typically correspond to the product of the
number of observations from both sides, as each pair of observations will
be linked with a single line.