How to add a new trace while removing the last one? - r

Question

I am new to shiny and plotly. What I'm trying to do is to add a trace first and then I want it to be replaced by a new one every time I click on a button.
here is my minimal example:
library(shiny)
library(plotly)
ui <- fluidPage(plotlyOutput("fig1"),
numericInput("A",
label = h5("A"),
value = "",
width = "100px"),
numericInput("B",
label = h5("B"),
value = "",
width = "100px"),
actionButton("action3", label = "Add to plot"),
actionButton("action4", label = "Remove point")
)
server <- function(input, output) {
A <- 1:5
B <- c(115, 406, 1320, 179, 440)
data <- data.frame(A, B)
fig <- plot_ly(data, x = A, y = B, type = 'scatter', mode = 'markers')
output$fig1 <- renderPlotly(fig)
observeEvent(input$action3, {
vals <- reactiveValues(A = input$A, B = input$B)
plotlyProxy("fig1") %>%
plotlyProxyInvoke("addTraces",
list(x = c(vals$A,vals$A),
y = c(vals$B,vals$B),
type = "scatter",
mode = "markers"
)
)
})
observeEvent(input$action4, {
vals <- reactiveValues(A = input$A, B = input$B)
plotlyProxy("fig1") %>%
plotlyProxyInvoke("deleteTraces")
})
}
shinyApp(ui,server)
I can add a new trace easily but they all remain on the plot.
My solution was to add a new button to delete the trace but it did not work.
I have already read this but I couldn't make it work.

Answer 1

Based on what you described, it sounds like you want to add a trace and remove the most recent trace added at the same time when the button is pressed. This would still leave the original plot/trace that you started with.
I tried simplifying a bit. The first plotlyProxyInvoke will remove the most recently added trace (it is zero-indexed, leaving the first plotly trace in place).
The second plotlyProxyInvoke will add the new trace. Note that the (x, y) pair is included twice based on this answer.
library(shiny)
library(plotly)
A <- 1:5
B <- c(115, 406, 1320, 179, 440)
data <- data.frame(A, B)
ui <- fluidPage(plotlyOutput("fig1"),
numericInput("A",
label = h5("A"),
value = "",
width = "100px"),
numericInput("B",
label = h5("B"),
value = "",
width = "100px"),
actionButton("action3", label = "Add to plot"),
)
server <- function(input, output, session) {
fig <- plot_ly(data, x = A, y = B, type = 'scatter', mode = 'markers')
output$fig1 <- renderPlotly(fig)
observeEvent(input$action3, {
plotlyProxy("fig1", session) %>%
plotlyProxyInvoke("deleteTraces", list(as.integer(1)))
plotlyProxy("fig1", session) %>%
plotlyProxyInvoke("addTraces",
list(x = c(input$A, input$A),
y = c(input$B, input$B),
type = 'scatter',
mode = 'markers')
)
})
}
shinyApp(ui,server)