R - Text Formatting of Plot Label Text - Strikethrough

Question

How does one make a portion of label text have strikethrough in a plot label?

For example, to get the y-axis-label to read "strikethrough text in a label?"

 ggplot(mpg, aes(x=displ, y=hwy)) 
        + geom_point() 
        + ylab("~~strikethrough~~ text in a label?")

Pretty small question that I thought would be pretty trivial to find a solution too, but no avail after a while of looking.

Answer 1

You can create a custom element function for axis.text.y. I tried to get a general solution but I think my solution is a little bit tricky and not very clean since I had to set manually the y position of some viewport(see the code for better explanation)

The custom axis.text.y had 2 arguments : the axis label and the text to strike through it. It finds the position of the text to strike with the axis label and add a segment.(If the text is defined twice it would take only the first occurrence).

To use the solution you can do something like this:

library(ggplot2)
library(grid)
ggplot(mpg, aes(x=displ, y=hwy)) +
    geom_point() + theme(axis.title.y=element_blank())+
    theme( axis.text.y = axis.strike(strike = "label",
               lab="strikethrough text in a label?"))

the code of the custom axis.text.y element:

# user interface : element called by the user
axis.strike = function(strike,lab) {
    structure(
        list(strike=strike,lab=lab),
        ## inheritance since it should be a element_text
        class = c("element_custom","element_blank")  
    )
}

element_grob.element_custom <- function(element, x,y)  {
    ## the axis label
    g.X <- textGrob(element$lab,rot=90,vjust=-0.25)
    ## I use the grob text dimensions(height,width,position) to 
    ## create a viewport vp
    ## within this viewport I create a segment 
    unit.H <- grobHeight(g.X)
    unit.W <- grobWidth(g.X)
    rate <- nchar(element$strike)
    ## search of the position of the text to strike
    pos <- as.numeric(gregexpr(element$strike,element$lab)[[1]])
    vp=viewport(just="centre",
          ##BAD OFFSET HERE!!
          ## TODO: find better way to define viewport y position
           y = grobY(g.X,'south')+unit(5,'line'), 
           yscale=c(0,nchar(element$lab)),
          width =unit.W,height=unit.H)
    g.seg <- segmentsGrob(vp=vp,x0=0,x1=0,
                           y0=unit(pos-1,'native'),
                           y1=unit(pos-1+rate,'native'))
    gTree(children=gList(g.seg,g.X,g.seg),cl = "custom_axis")
}