Create new axis at the center of the graph: ggplot

Question

I want to create a new axis for an existing plot. I can use the geom_line layer for this but how do I add labels for X and Y axis (similar to the default axis).

Answer 1

One option would be ggh4x::coord_axes_inside which offers an out-of-box option to add inside axes:

library(ggplot2)
library(ggh4x)

iris |>
  ggplot(aes(Sepal.Length, Sepal.Width, color = Species)) +
  geom_point() +
  theme(axis.line = element_line()) +
  coord_axes_inside(
    labels_inside = TRUE,
    xintercept = 6,
    yintercept = 3
  )