Shiny Plotly reactive data plot

I've put together this Shiny app from tutorial and examples, and I've become stuck. My aim is to make the plot reactive, so that the data points in 'uval$df' are plotted, meaning that selected points will be removed from the graph, and it can't be selected twice. How do I do this? (I've got a feeling it's something lacking in my basic understanding)

Thanks!

library(shiny)
library(plotly)
library(dplyr)

ui <- fluidPage(
  fluidRow(
    column(12,plotlyOutput("plot"),
           verbatimTextOutput("txtout1"),
           verbatimTextOutput("txtout2"),
           verbatimTextOutput("txtout3"))
  )
)

server <- function(input, output, session) {
x<-c(1,2,34,2,1,23,24)   
y<-c(10,20,30,40,50,60,70)
df<-data.frame(x,y)
vector.is.empty <- function(x) return(length(x) ==0 )

K <-reactive({
  event_data("plotly_selected",source = "B")
})

M<-reactive({
  K()[,c("x","y")]
})

values <- reactiveValues()
values$df <- data.frame(x = numeric(0), y = numeric(0))
newEntry <- observeEvent(K(),priority = 1,{
    new0 <- isolate(M())
    isolate(values$df <- rbind(values$df, new0))
})

uval <- reactiveValues()
uval$df <- df
newEntry1 <- observeEvent({values$df},priority = 2,{
  new1 <- isolate(data.frame(values$df))
  isolate(uval$df <- setdiff(df,new1))
})

output$plot <- renderPlotly({
  plot_ly(x = df$x, y = df$y, mode = "markers",source="B") %>%
    layout(dragmode =  "select", title = "Original Plot", font=list(size=10))
})

output$txtout1 <- renderPrint({
  if(vector.is.empty(K())) "Click and drag across points" else M()
})

output$txtout2 <- renderPrint({
  uval$df
})

output$txtout3 <- renderPrint({
  values$df
})

}

shinyApp(ui, server, options = list(display.mode = "showcase"))