How to prevent mouse over labels to disappear in plot interactions when not moving the mouse?

[Jannik Vindeløv]

Dear Shiny experts

I want to show a mouse-over label when a user interacts with my plot, but in the script below, the label will disappear after a short while, even though the mouse is not moved:

library(shiny)
library(tidyverse)

ui <- basicPage(
  plotOutput("plot1",
  hover = "plot_hover"),
  verbatimTextOutput("info")
)

server <- function(input, output) {
  output$plot1 <- renderPlot({
  
  hover_data <- nearPoints(mtcars, input$plot_hover) %>% 
  mutate(label = paste(mpg, cyl, disp, hp, sep = "\n"))
  
  mtcars %>%
  ggplot(aes(x = wt, y = mpg))+
  geom_point()+
  geom_label(data = hover_data, aes(label = label), nudge_x = 0.2)
  })

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

shinyApp(ui, server)

I assume it is an issue with reactivity, but I fail to find the solution.

Any help will be greatly appreciated!

/Jannik

[Stephen McDaniel]

Hi Jannik,

Please find a solution here: https://github.com/Stephen-McDaniel/ggplot-hover-values-disappear

This solution starts with an initial, non-reactive ggplot object,
   an initial reactive plot output object,
   and an observeEvent for the hover item, this triggers
   a graph update with the hover as well as text info dialog updates.

Best regards,
Stephen McDaniel

Chief Data Scientist

PowerTrip Analytics

Automatic data, analytic & visualization solutions in the cloud

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[Jannik Vindeløv]

Dear Stephen

This was exactly what I needed.

However, I'm still puzzled why the hover event clears itself in my example (this is not the case in the shiny example https://shiny.rstudio.com/articles/plot-interaction.html)?

Could it be that, because the plot updates, input$plot_hover fails to find a value and becomes NULL?

Thanks a lot for this solution.

/Jannik

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[Stephen McDaniel]

Hi Jannik,

I am certain one of the developers at RStudio could better explain it.

This type of output is an image with an mouse location observational layer on top of it. By updating other elements within the same reactive, it appears to reset the hover event and clear the value until another hover event is generated.

Here is the png from the render with a working hover in my solution example.

For example, just the info output your example can work if you remove the hover label from the plot1 reactive and move the nearPoints function to the info output.

library(shiny)
library(tidyverse)

ui <- basicPage(
  plotOutput("plot1",
  hover = "plot_hover"),
  verbatimTextOutput("info")
)

server <- function(input, output) {
  output$plot1 <- renderPlot({
 

     mtcars %>%
        ggplot(aes(x = wt, y = mpg))+

        geom_point()#+
        #geom_label(data = hover_data, aes(label = label), nudge_x = 0.2)
    
  })

  output$info <- renderText({

    hover_data <- nearPoints(mtcars, input$plot_hover) %>%
       mutate(label = paste(mpg, cyl, disp, hp, sep = "\n"))

    paste0("x=", input$plot_hover$x, "\ny=", input$plot_hover$y)
  })
}

shinyApp(ui, server)

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