Interactive shiny app returns wrong coordinates

Question

I'm trying to use Shiny to create an interactive scatter plot where I can click on any point on the graph and get the corresponding x and y co-ordinates. It works (i.e. is the RStudio example) for base graphics (commented out) gives different and incorrect numbers using ggplot.

library(shiny)
library(ggplot2)

ui <- basicPage(
  plotOutput("plot1", click = "plot_click"),
  verbatimTextOutput("info")
)

server <- function(input, output) {
  output$plot1 <- renderPlot({
    # plot(mtcars$wt, mtcars$mpg)
    g=ggplot(mtcars,aes(wt,mpg))+geom_point()
    g

  })

  output$info <- renderText({
    paste0("x=", input$plot_click$x, "\ny=", input$plot_click$y)
  })
}

shinyApp(ui, server)

Do I need to add anything to my code?

Interesting that it worked for correctly for you. On my machine I get numbers up in the hundreds, possibly pixels. I wonder if there is something wrong with my installation. Have in the meantime a hack (posted below) but is is hardly elegant. — drw, Aug 18 '17 at 17:04
Your code works correctly under R and R studio. I am using ggplot2_2.2.1 and shiny_1.0.4. And you ? You second code does not work on my R. — Marco Sandri, Aug 18 '17 at 17:09

score 1 · Answer 1 · answered Aug 18 '17 at 17:02

One possible hack is to print the ggplot2 object to the screen with print() which then seems to return coordinates in [0,1]. If you note down the plotting limits before, you can then calculate the desired values.

library(shiny)
library(ggplot2)

ui <- basicPage(
  plotOutput("plot1", click = "plot_click"),
  verbatimTextOutput("info")
)

server <- function(input, output) {
  output$plot1 <- renderPlot({
    # plot(mtcars$wt, mtcars$mpg)
    g=ggplot(mtcars,aes(wt,mpg))+geom_point()


    # works from version 0.8.9 on: https://stackoverflow.com/questions/7705345/how-can-i-extract-plot-axes-ranges-for-a-ggplot2-object
    a=ggplot_build(g)$layout$panel_ranges[[1]]
    x.range <<- a$x.range
    y.range <<- a$y.range

    print(g)

  })

  output$info <- renderText({

    paste0("x=", x.range[1]+diff(x.range)*input$plot_click$x,
           "\ny=", y.range[1]+diff(y.range)*input$plot_click$y)
  })
}

shinyApp(ui, server)

This works but is obviously full of things that might go wrong. Not sure if this is the best way.

Note comments section to question. This solution did not work for some users. — drw, Aug 19 '17 at 09:22
As in main answer the issue appears to have been a version issue. With the versions updated to above hack is not only unnecessary but also does not work. — drw, Aug 21 '17 at 10:39

score 0 · Accepted Answer · answered Aug 21 '17 at 10:37

With many thanks for Marco's comment, this was indeed a version number issue. Updating to the most recent Shiny version resolved the problem. Now the 'correct' version works whilst my hack, as for Marco, does not. I'm now on Shiny 1.0.4 and ggplot2 2.2.0.

Interactive shiny app returns wrong coordinates

2 Answers2