Adding arrows to ggswim

It can be useful to visually indicate the continuation of specific records in a swimmer plot. Optionally adding arrows to the tail ends of swimmer plot lanes in ggswim can help communicate subject survival status, such as whether or not a subject is still on a given study.

To facilitate the addition of arrows, we provide the add_arrows() function as a way to tack on these continuation indicators to your swimmer plot lanes. Behind the scenes, the inclusion of arrows is facilitated by a call to ggplot2::geom_segment() and creates a new ggplot2 layer with a ggswim_arrows flag. add_arrows() sets the segment length to 0, so that assigned arrows are always placed on the right side of indicated subjects. add_arrows() gives users have full control over arrow neck and head length, along with options for color, fill, and type (refer to ?add_arrows for detailed information).

Adding arrows using `add_arrows()`

To demonstrate how you might add arrows onto the patient_data dataset, let’s take a sample subset of patient_data that would help us make use of add_arrows():

arrow_data |>
  rmarkdown::paged_table()

This should look familiar, a pared-down dataset with a status column that we’ll use to flag which lanes of our swimmer plot should have arrows. Now let’s use add_arrows() in combination with ggswim() to make a swimmer plot:

patient_data |>
  ggswim(
    mapping = aes(
      x = start_time, xend = end_time, y = pt_id,
      color = disease_assessment
    ),
    linewidth = 5
  ) +
  add_arrows(
    data = arrow_data,
    mapping = aes(xend = end_time, y = pt_id),
    arrow = status,
    arrow_neck_length = 5,
    arrow_colour = "slateblue",
    arrow_fill = "cyan"
  )

Adding arrows using add_arrows()

Adding arrows using `add_arrows()`