Changing pallete values based on input

Question

I'm using leaflet and shiny. I would like to color my markers based on a column that can be changed via input. It's almost the same as Modifying Existing Maps with leafletProxy. In this example, the user can change the color palette. In my example, I would like to change the column that the palette is applied on. I'm trying to use something like:

fillColor = ~pal(!!sym(input$col_to_apply)) # input$col_to_apply is a column name (string) I want to use

However, this doesn't work. I'm also not sure if I have to use reactive() in this case.

Answer 1

Sure. My suggestion would be to do it before the palette is created. Palettes are tricky enough as it is. See the below minimal example:

library(leaflet)
library(maps)
library(shiny)

ui <- fluidPage(

    leafletOutput("map_1"),

    selectInput(inputId = "input_species", label = "Species Selection", choices = c("Species_1", "Species_2", "Species_3"))

)


server <- function(input, output, session) {

    #Load a map of the US from the 'map' package (runs once when apps starts)
    shp_map = map("state", fill = TRUE, plot = FALSE)

    #Make up a dataframe with some data for three species for each state (runs once when apps starts)
    df_data <- data.frame(state = unique(shp_map$names), Species_1 = sample(100:199, 63), Species_2 = sample(200:299, 63), Species_3 = sample(300:399, 63))

    #Create map
    output$map_1 <- renderLeaflet({

        df_map <- df_data

        #Create a column called species selected based on which is selected in the dropdown box
        df_map$Species_Selected <- df_map[, paste(input$input_species)]

        #Create a palette function
        palette <- colorNumeric(palette = "Blues", domain = df_map$Species_Selected)

        #Use the palette function created above to add the appropriate RGB value to our dataframe
        df_map$color <- palette(df_map$Species_Selected)

        #Create map
        map_1 <- leaflet(data = shp_map) %>% 

            addPolygons(fillColor = df_map$color, fillOpacity = 1, weight = 1, color = "#000000", popup = paste(sep = "", "<b>", paste(shp_map$names), " ", "</b><br>", df_map$Species_Selected)) 

        map_1

    })

}

shinyApp(ui, server)