Leaflet with Shiny: reacting to input$map_zoom with leafletProxy()
Andrew Caines
library(shiny)
library(leaflet)
library(RColorBrewer)
ui <- bootstrapPage(
tags$style(type = "text/css", "html, body {width:100%;height:100%}"),
leafletOutput("map", width = "100%", height = "100%"),
absolutePanel(top = 10, right = 10,
sliderInput("range", "Magnitudes", min(quakes$mag), max(quakes$mag),
value = range(quakes$mag), step = 0.1
),
selectInput("colors", "Color Scheme",
rownames(subset(brewer.pal.info, category %in% c("seq", "div")))
),
checkboxInput("legend", "Show legend", TRUE)
)
)
server <- function(input, output, session) {
# Reactive expression for the data subsetted to what the user selected
filteredData <- reactive({
quakes[quakes$mag >= input$range[1] & quakes$mag <= input$range[2],]
})
# This reactive expression represents the palette function,
# which changes as the user makes selections in UI.
colorpal <- reactive({
colorNumeric(input$colors, quakes$mag)
})
output$map <- renderLeaflet({
# Use leaflet() here, and only include aspects of the map that
# won't need to change dynamically (at least, not unless the
# entire map is being torn down and recreated).
leaflet(quakes) %>% addTiles() %>%
fitBounds(~min(long), ~min(lat), ~max(long), ~max(lat))
})
## AC: collects map zoom value
mapzoom <- reactive({
input$map_zoom
})
# Incremental changes to the map (in this case, replacing the
# circles when a new color is chosen) should be performed in
# an observer. Each independent set of things that can change
# should be managed in its own observer.
observe({
pal <- colorpal()
## AC: circle radius set to equal map zoom
circleRadius <- mapzoom()
leafletProxy("map", data = filteredData()) %>%
clearShapes() %>%
## AC: radius = circle radius
addCircles(radius = circleRadius, weight = 1, color = "#777777",
fillColor = ~pal(mag), fillOpacity = 0.7, popup = ~paste(mag)
)
})
# Use a separate observer to recreate the legend as needed.
observe({
proxy <- leafletProxy("map", data = quakes)
# Remove any existing legend, and only if the legend is
# enabled, create a new one.
proxy %>% clearControls()
if (input$legend) {
pal <- colorpal()
proxy %>% addLegend(position = "bottomright",
pal = pal, values = ~mag
)
}
})
}
shinyApp(ui, server)
