Group geom_vline for a conditional-CodePudding

I believe I'm going about this incorrectly. I have a ggplot that has several lines graphed into it. Each line is categorized under a 'group.' (ie. predator lines include lines for bear frequency, lion_frequency; prey lines include lines for fish frequency, rabbit_frequency; etc.)

Here's a reproducible example using dummy data

p <- function(black_lines, green_lines){
  ggplot(mtcars, aes(x = wt, y = mpg))   geom_point()  
  geom_vline(xintercept = 5)  
  geom_vline(xintercept = 10)  
  geom_vline(xintercept = 1:5,
             colour = "green",
             linetype = "longdash")
}

p()

Ideally, it would work like:

p <- function(black_lines, green_lines){
  ggplot(mtcars, aes(x = wt, y = mpg))   geom_point()  
  
  if (black_lines){
    geom_vline(xintercept = 5)  
    geom_vline(xintercept = 10)  
  }
  
  if(green_lines){
  geom_vline(xintercept = 1:5,
             colour = "green",
             linetype = "longdash")
  }
}

p(T, T)

This method won't work, of course since R doesn't like -> Error in ggplot_add(): ! Cannot add ggproto objects together. Did you forget to add this object to a ggplot object?

But I'm wondering if this is possible? I couldn't find any similar questions so I feel like I'm going about wrongly.

For those who believe more context is needed. This is for a reactive Shiny app and I want the user to be able to select how the graph will be generated (as such with specific lines or not).

Thank you for your guidance in advance!

CodePudding user response：

You could create your conditional layers using an if and assign them to a variable which could then be added to your ggplot like any other layer:

Note: In case you want to include multiple layers then you could put them in a list, e.g. list(geom_vline(...), geom_vline(...)).

library(ggplot2)

p <- function(black_lines, green_lines){
  vline_black <- if (black_lines) geom_vline(xintercept = c(5, 10))
  vline_green <- if (green_lines) geom_vline(xintercept = 1:5,
                                             colour = "green",
                                             linetype = "longdash")
  
  ggplot(mtcars, aes(x = wt, y = mpg))   
    geom_point()  
    vline_black  
    vline_green
}

p(T, T)


p(T, F)