includeHTML in R Shiny Leaflet popups

Question

I'm making an R Shiny app with Leaflet that shows trees in a city. I want to add an svg image to the marker popups that depends on the tree species for the clicked marker, but I can't get includeHTML to work.

Minimal reproducible example with two markers

circle.svg:

<svg width = "20" height = "20"
  xmlns="http://www.w3.org/2000/svg">
  <circle cx="10" cy="10" r="10" style="fill:#000;"/>
</svg>

square.svg:

<svg width = "20" height = "20"
  xmlns="http://www.w3.org/2000/svg">
  <rect x="0" y="0" width = "20" height = "20" style="fill:#000;"/>
</svg>

When I run the code below, I get an error:

library(shiny)
library(leaflet)
library(tidyverse)
library(magrittr)

df <- data.frame("type" = c("circle", "square"), 
                 "lon" = c(13.36, 13.37), 
                 "lat" = c(52.56, 52.57)
                 )

ui <- fluidPage(

  leafletOutput("map")

)

server <- function(input, output) {

  output$map <- renderLeaflet({
    leaflet(df) %>%
      addTiles() %>%
      addCircleMarkers(
        popup = ~ paste0(type, ": ", includeHTML(paste0(type, ".svg")))
        )
  })

}
shinyApp(ui = ui, server = server)

Warning: Error in file: invalid 'description' argument
  119: file
  118: readLines
  117: includeHTML
...

But if remove includeHTML, the filenames are written correctly in the popups.

popup = ~ paste0(type, ": ", paste0(type, ".svg"))

If I index type, includeHTML works fine, expect it shows the circle in both popups, which is of course not what I want:

popup = ~ paste0(type, ": ", includeHTML(paste0(type[1], ".svg")))

It seems the includeHTML takes the whole df$type vector instead of just the one element of the vector that is relevant to the marker.

What is going on, and how can I solve this? Help is very much appreciated.

Answer 1

You can generate your popups using
sapply(type, function(x) paste0(x, ": ", includeHTML(paste0(x, ".svg"))))
as follows:

ui <- fluidPage(
  leafletOutput("map")
)

server <- function(input, output) {
  output$map <- renderLeaflet({
    leaflet(df) %>%
      addTiles() %>%
      addCircleMarkers(
        popup=~sapply(type, function(x) paste0(x, ": ", includeHTML(paste0(x, ".svg"))))
        )
  })
}

shinyApp(ui = ui, server = server)