library(ggplot2)
ui <- basicPage(
  plotOutput("plot1", click = "plot_click"),
  verbatimTextOutput("info")
)

server <- function(input, output) {
  output$plot1 <- renderPlot({
    ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point()
  })
  
  output$info <- renderPrint({
    # With ggplot2, no need to tell it what the x and y variables are.
    # threshold: set max distance, in pixels
    # maxpoints: maximum number of rows to return
    # addDist: add column with distance, in pixels
    nearPoints(mtcars, input$plot_click, threshold = 10, maxpoints = 1,
               addDist = TRUE)
  })
}

shinyApp(ui, server)