Why does addPolylines work differently on an R Shiny leaflet map? - r

Question

I have R code which creates a leaflet map with points connected by addPolylines().
library(shiny)
library(leaflet)
station = c("A", "B", "C", "D", "E", "F")
latitude = c(-1.63, -1.62, -1.62, -1.77, -1.85, -1.85)
longitude = c(34.3, 34.4, 34.7, 34.3, 34.5, 34.7)
big = c(0, 20, 60, 90, 50, 10)
small = c(100, 80, 40, 10, 50, 90)
colour = c("blue", "blue", "red", "red", "black", "black")
group = c("A", "A", "B", "B", "C", "C")
df = cbind.data.frame(station, latitude, longitude, big, small, colour, group)
colnames(df) = c("station", "latitude", "longitude", "big", "small", "colour", "group")
myMap = leaflet() %>%
setView(lng = 34.4, lat = -1.653, zoom = 8) %>%
addTiles()%>%
addCircles(data = df,
lng = ~ longitude, lat = ~ latitude,
color = ~ colour,
radius = 2000,
stroke = TRUE,
opacity = 5,
weight = 1,
fillColor = ~ colour,
fillOpacity = 1)
for(group in levels(df$group)){
myMap = addPolylines(myMap,
lng= ~ longitude,
lat= ~ latitude,
data = df[df$group == group,],
color= ~ colour,
weight = 3)
}
myMap
This is exactly what I am wanting and it looks like this:
However, when I put this into an R shiny app, the map will not appear. The ui code is:
fluidPage(
theme = shinythemes::shinytheme("yeti"),
titlePanel(title = "Polyline Map"))
mainPanel("",
helpText("This is the polyline map"),
hr(),
leafletOutput("myMap", height = 400, width = 600)
)
The server code is:
function(input, output, session) {
output$myMap = renderLeaflet({
leaflet() %>%
setView(lng = 34.4, lat = -1.653, zoom = 8) %>%
addTiles()%>%
addCircles(data = df,
lng = ~ longitude, lat = ~ latitude,
color = ~ colour,
radius = 4000,
stroke = TRUE,
opacity = 5,
weight = 1,
fillColor = ~ colour,
fillOpacity = 0.5)
for(group in levels(df$group)){
myMap = addPolylines(myMap,
lng= ~ longitude,
lat= ~ latitude,
data = df[df$group==group,],
color= ~ colour,
weight = 3)
}
}
)}
And the global code is:
library(shiny)
library(leaflet)
station = c("A", "B", "C", "D", "E", "F")
latitude = c(-1.63, -1.62, -1.62, -1.77, -1.85, -1.85)
longitude = c(34.3, 34.4, 34.7, 34.3, 34.5, 34.7)
big = c(0, 20, 60, 90, 50, 10)
small = c(100, 80, 40, 10, 50, 90)
colour = c("blue", "blue", "red", "red", "black", "black")
group = c("A", "A", "B", "B", "C", "C")
df = cbind.data.frame(station, latitude, longitude, big, small, colour, group)
colnames(df) = c("station", "latitude", "longitude", "big", "small", "colour", "group")
Does anyone know why this happens and what I can do to fix it? Thank you!

Answer 1

I was able to get your code working with two very small adjustments:
You refer to myMap in your renderLeaflet function but that is not defined yet, so I modified the first line to myMap <- leaflet() %>%
You do not return anything from the renderLeaflet function, so I added the statement myMap after the for-loop.
Working code is shown below, hope this helps!
library(shiny)
library(leaflet)
station = c("A", "B", "C", "D", "E", "F")
latitude = c(-1.63, -1.62, -1.62, -1.77, -1.85, -1.85)
longitude = c(34.3, 34.4, 34.7, 34.3, 34.5, 34.7)
big = c(0, 20, 60, 90, 50, 10)
small = c(100, 80, 40, 10, 50, 90)
colour = c("blue", "blue", "red", "red", "black", "black")
group = c("A", "A", "B", "B", "C", "C")
df = cbind.data.frame(station, latitude, longitude, big, small, colour, group)
colnames(df) = c("station", "latitude", "longitude", "big", "small", "colour", "group")
ui <- fluidPage(
theme = shinythemes::shinytheme("yeti"),
titlePanel(title = "Polyline Map"),
mainPanel("",
helpText("This is the polyline map"),
hr(),
leafletOutput("myMap", height = 400, width = 600)
)
)
server <- function(input, output, session) {
output$myMap = renderLeaflet({
myMap <- leaflet() %>%
setView(lng = 34.4, lat = -1.653, zoom = 8) %>%
addTiles()%>%
addCircles(data = df,
lng = ~ longitude, lat = ~ latitude,
color = ~ colour,
radius = 4000,
stroke = TRUE,
opacity = 5,
weight = 1,
fillColor = ~ colour,
fillOpacity = 0.5)
for(group in levels(df$group)){
myMap = addPolylines(myMap,
lng= ~ longitude,
lat= ~ latitude,
data = df[df$group==group,],
color= ~ colour,
weight = 3)
}
myMap
})
}
shinyApp(ui,server)