Shiny error while using nearPoints in renderPlotly click event - r

Question

I would like to fetch nearPoints using the data from a click event.
I have found the below snippet from the Shiny webpage and it works fine as expected.
output$plot <- renderPlot({
d <- data()
plot(d$speed, d$dist)
})
output$plot_clickedpoints <- renderPrint({
# For base graphics, we need to specify columns, though for ggplot2,
# it's usually not necessary.
res <- nearPoints(data(), input$plot_click, "speed", "dist")
if (nrow(res) == 0)
return()
res
})
I tried to mimic the above the approach to identify the nearPoints in the Plotly plots using the click event data. However, it did not work.
output$plot <- renderPlotly({
d <- data()
plot(d$speed, d$dist)
})
output$plot_clickedpoints <- renderPrint({
# For base graphics, we need to specify columns, though for ggplot2,
# it's usually not necessary.
res <- nearPoints(data(), event_data("plotly_click"), "speed", "dist")
if (nrow(res) == 0)
return()
res
})
Any idea on how to pass the coordinate information to the plotly plot?

Answer 1

I am not sure on how to do this with the nearPoints function, but is using that function really necessary? You could find the points that are within a threshold of the clicked point as well with the following code:
library(shiny)
library(plotly)
library(DT)
threshold_mpg = 3
threshold_cyl = 1
shinyApp(
ui <- shinyUI(
fluidPage(
plotlyOutput("plot"),
DT::dataTableOutput("table")
)
),
function(input,output){
data <- reactive({
mtcars
})
output$plot <- renderPlotly({
d <- data()
plot_ly(d, x= ~mpg, y=~cyl, mode = "markers", type = "scatter", source="mysource")
})
output$table<- DT::renderDataTable({
event.data <- event_data("plotly_click", source = "mysource")
print(event.data)
if(is.null(event.data)) { return(NULL)}
# A simple alternative for the nearPoints function
result <- data()[abs(data()$mpg-event.data$x)<=threshold_mpg & abs(data()$cyl-event.data$y)<=threshold_cyl, ]
DT::datatable(result)
})
}
)
Hope this helps.

Answer 2

The "plotly_selected" plotly.js event returns more information than event_data("plotly_selected") actually gives you, including coordinate information (this was arguably a design mistake made by event_data() that's too late to change). Fortunately, if you know a bit of JavaScript, know how to listen to plotly select events, and how to send data from client to a shiny server, you can do something like this to access that info:
library(shiny)
library(plotly)
library(htmlwidgets)
ui <- fluidPage(
plotlyOutput("p"),
verbatimTextOutput("info")
)
server <- function(input, output, session, ...) {
output$p <- renderPlotly({
plot_ly(x = 1:10, y = 1:10) %>%
layout(dragmode = "select") %>%
onRender(
"function(el, x) {
var gd = document.getElementById(el.id);
gd.on('plotly_selected', function(d) {
// beware, sometimes this event fires objects that can't be seralized
console.log(d);
Shiny.onInputChange('my-select-event', d.range)
})
}")
})
output$info <- renderPrint({
print(session$rootScope()$input[["my-select-event"]])
})
}
shinyApp(ui, server)
Using the coordinate information you could write a function that works in a similar way to nearPoints().