Shiny Mouse Click with ggplot2 pie chart

Question

I know that I can get xy mouse click coordinates in shiny with this stacked bar chart produced by ggplot2:

data <- data.frame(pie = c(0.25,0.25,0.25,0.25))
library(ggplot2)
ui <- fluidPage(
  plotOutput('pie', click = "plot_click"),
  verbatimTextOutput('mouse')
)

server <- function(input, output) {
    output$pie <- renderPlot({
        ggplot(data, aes(x = factor(1), y = pie, fill = row.names(data))) 
              + geom_bar(stat = "identity")
})
    output$mouse <- renderPrint({
        str(input$plot_click)
    })
}

shinyApp(ui=ui, server=server) 

Which when I ran and clicked on just now, I get this kind output, specifically a list, which contains the relative xy coordinate that I clicked on in the plot:

List of 7
$ x      : num 0.887
$ y      : num 0.116
$ mapping:List of 3
 ..$ x   : chr "factor(1)"
 ..$ y   : chr "pie"
 ..$ fill: chr "row.names(data)"
$ domain :List of 4
 ..$ left  : num 0.5
 ..$ right : num 1.5
 ..$ bottom: num -0.05
 ..$ top   : num 1.05
$ range  :List of 4
 ..$ left  : num 44.9
 ..$ right : num 818
 ..$ bottom: num 365
 ..$ top   : num 5.48
$ log    :List of 2
 ..$ x: NULL
 ..$ y: NULL
$ .nonce : num 0.797

However, when I convert this to a pie chart instead with the following, I don't get a list with int 0 elements for the x and y. I'm using this code (which simply adds coord_polar(theta = "y") to the ggplot):

data <- data.frame(pie = c(0.25,0.25,0.25,0.25))
library(ggplot2)
ui <- fluidPage(
  plotOutput('pie', click = "plot_click"),
  verbatimTextOutput('mouse')
)

server <- function(input, output) {
    output$pie <- renderPlot({
        ggplot(data, aes(x = factor(1), y = pie, fill = row.names(data))) 
            + geom_bar(stat = "identity") 
            + coord_polar(theta = "y")
    })
    output$mouse <- renderPrint({
        str(input$plot_click)
    })
 }

shinyApp(ui=ui, server=server) 

Which gives me this kind of result upon clicking on the plot:

List of 7
$ x      : int 0
$ y      : int 0
$ mapping:List of 3
 ..$ x   : chr "factor(1)"
 ..$ y   : chr "pie"
 ..$ fill: chr "row.names(data)"
$ domain :List of 4
 ..$ left  : NULL
 ..$ right : NULL
 ..$ bottom: NULL
 ..$ top   : NULL
$ range  :List of 4
 ..$ left  : num 31.9
 ..$ right : num 818
 ..$ bottom: num 373
 ..$ top   : num 5.48
$ log    :List of 2
 ..$ x: NULL
 ..$ y: NULL
$ .nonce : num 0.964

I'm new to using these mouse events for plots. Is there any way to get the mouse click coordinates for a ggplot pie chart? If it's not possible, is there a way to use javascript to covert the pixel coordinates of where I click to plot coordinates? Or, is there a better graphics system that would support this kind of functionality that I could use in shiny?

Thanks in advance!

Answer 1

There doesn't seem to be an easy answer to this question, without resorting to graphics and web programming outside of R.

My solution was to create a legend for the plot out of html, where the user clicks a part of the legend in order to derive which data they selected.