Leaflet and Shiny "could not find function leafletOutput()" - r

Question

I have a leaflet map and I want the option of switching from the values of A being mapped to the values of B. Every example I can find says to use shiny and leaflet and all of these examples include something along the lines of:
ui <- fluidPage(
selectInput(inputId = "Data",
label = "Data",
choices = c("A","B"),
leafletProxy(outputId = "map") #or leafletOutput
))
but I keep getting the error that
leafletProxy (or leafletOutput)does not exist
. How do I solve this? My leaflet is created with :
mypal <- colorNumeric(palette = "viridis", domain = d$A)
leaflet() %>%
addProviderTiles("OpenStreetMap.Mapnik") %>%
setView(lat = 39.8283, lng = -98.5795, zoom = 4) %>%
addPolygons(data =
USA, stroke = TRUE, color='black', opacity=1, weight=.5, smoothFactor = 0.2, fillOpacity = 1,
fillColor = ~mypal(d$A),
popup = paste('<b>',d$state, "</b><br>A:", d$A) %>%
addLegend(position = "bottomleft", pal = mypal, values = d$A,
title = "A",
opacity = 1)

Answer 1

It seems from your example that your shiny has no server function, so it is not going to work.
Please, find attached a mock shiny you can start building on:
library(shiny)
library(leaflet)
ui <- fluidPage(
selectInput(inputId = "Data",
label = "Data",
choices = c("A", "B")),
leafletOutput("map")
)
server <- server <- function(input, output, session) {
output$map <- renderLeaflet({
if((input$Data) == "A"){
point = c(42.6525, -73.757222)
}
if((input$Data) == "B"){
point = c(39.283333, -76.616667)
}
leaflet() %>%
addProviderTiles("OpenStreetMap.Mapnik") %>%
addMarkers(lat = point[1], lng = point[2])
})
It will show "Albany" when you select "A" and Baltimore when you select "B"
Basically:
ui is kind of the "interface", what it is going to be shown:
selectInput: you can choose A or B here
leafletOutput: will show the leaflet map
server will do the "hard job" of creating the map and computing actions when you use selecInput:
output$map means that we want to render the leafletOuput (that is why it is called map, as in leafletOutput("map")
Then, according to the input selected (A or B)
if((input$Data) == "A"){
point = c(42.6525, -73.757222)
}
if((input$Data) == "B"){
point = c(39.283333, -76.616667)
}
We assign coordinates of Albany or Baltimore to point.
Finally, we build the map:
leaflet() %>%
addProviderTiles("OpenStreetMap.Mapnik") %>%
addMarkers(lat = point[1], lng = point[2])
PLEASE, take into account that this is a mock shiny, it is far from perfect, it is only illustrative.
Best!