ggplot自定义主题中的条件参数

Question

I am developing a custom theme based on the 538 theme in ggthemes. I have a particular use case where I would like to conditionally change the legend text if I am preparing graphs about organisms. I want to make the legend text italics if I am reporting Genus species results.

Here is my theme so far:

theme_EPI <- function() {
  theme_fivethirtyeight(base_size = 14) %+replace%
    theme(
      panel.background  = element_blank(),
      plot.background = element_rect(fill = 'white', colour = NA),
      plot.title = element_text(size = 18),
      strip.text = element_text(size=14),
      legend.text = element_text(size = 12, face = 'italic'),
      legend.background = element_rect(fill="transparent", colour=NA),
      legend.key        = element_rect(fill="transparent", colour=NA),
      panel.grid.major.y = element_line(colour = 'grey90'),
      panel.grid.major.x = element_blank(),
      strip.background = element_blank()
    )
}

If have tried passing the parameter organism=TRUE to the the function call and then an ifelse(organism==TRUE, face='italic', 'face='plain') in the element_text .

Is this even possible in a custom theme?

Answer 1

Yes, this is definitely possible, you just have to slightly rethink how the ifelse() will work:

theme_EPI = function(organism = TRUE) {
   theme_dark() %+replace%
        # axis.title: labels for x and y axes
        theme(axis.title = element_text(
            face = ifelse(organism, 'italic', 'plain')
        ))
}

ggplot(iris, aes(Petal.Width, Petal.Length)) +
    geom_point() +
    theme_EPI()  # Default: organism = TRUE

ggplot(iris, aes(Petal.Width, Petal.Length)) +
    geom_point() +
    theme_EPI(organism = FALSE)