add a vertical line in ggplot

To add a vertical line in ggplot, you can follow these steps:

1. Create a data frame with the x-axis value where you want the vertical line to be placed.
2. Use the geom_vline() function in ggplot to add the vertical line, specifying the xintercept parameter as the x-axis value.
3. Provide any additional customization, such as line color, size, and linetype, within the geom_vline() function.

These steps will allow you to add a vertical line to your ggplot visualization.