Returning Values from handle_hover() or handle_click() in ggvis

I was just hoping to figure out how i can use handle_hover() or handle_click() to return a value outside of the environment of the visualization.

Ultimately i want to use this to return a key value so i can link two graphs onto a shiny application.

Using the example from the documentation, I have:

mtcars$id <- seq_len(nrow(mtcars))

hoveron<-function(data,...){
  testval<<-str(data)

  testval
}

mtcars %>% ggvis(~mpg, ~wt,key:=~id) %>% layer_points() %>%
  handle_hover(hoveron)

This returns

'data.frame':   1 obs. of  3 variables:

$ id : int 16

$ mpg: num 10.4

$ wt : num 5.42"

In the console

What would i need to do in order to return testval= 16

Many thanks!

Solution

I do not know if this will help, as it is not clear where do you want to return the key value. But here is a simple demonstration.

There are 2 plots in this shiny app. The second plot's points are green but if you hover on a point of the first plot whose id is 25 ( you can see the id's printed on the console ), the second plot's points turn red. I used the needed_val <- reactiveValues() to keep track if the testval is 25. You can access this value from another reactive() context.

The ui.R -

library(ggvis)
library(shiny)
shinyUI(
  mainPanel(
    ggvisOutput("plot"),
    ggvisOutput("plot2")
  )
)

server.R -

library(shiny)
library(dplyr)
library(ggvis)

shinyServer(function(input, output, session) {


needed_val <- reactiveValues(testval = 11)
mtcars$id <- seq_len(nrow(mtcars))

hoveron<-function(data, ...){
  needed_val$testval <- as.numeric(data$id)

  str(needed_val$testval)
}

mtcars %>% ggvis(~mpg, ~wt,key:=~id) %>% layer_points() %>%
  handle_hover(hoveron) %>% bind_shiny("plot")

dat2 <- reactive({
  if(needed_val$testval == 25){
    color <- "red"
  }
  else{
    color <- "green"
  }
  color
})

vis <- reactive({
mtcars %>% ggvis(~mpg, ~wt) %>% layer_points(fill := dat2())

}) %>% bind_shiny("plot2")


})

Let me know if its helpful.