How to fix geospatial mislabeling on leaflet map within R Shiny app? - r

Question

I made the following map from a data frame that contains the number of parole of each state from the years 1995-2015 per 100,000 as well as the spatial information for each state. I want to incorporate it into r shiny app to have a slider to be able to choose the specific year and view it. I got the slider to work and change the data and when you first run it works and gives you the appropriate state and number. However, when you move around the slider the geospatial labels start moving around using the reactive and different states start getting different states labels. Like the following:
The slider starts at the year 2000 and as you can see the if I move it around it, in this case 2014, now we have florida being labeled as Montana.
All these was done within the R shiny app. This is the code I have below. I have my leaflet map fully created outside the server.
server <- function(input, output) {
#Set YEAR with Slider
state_parole_year <- reactive({
state_parole %>%
filter(year == year(input$year))
})
labels_year <- reactive({paste("Parole/100000 US Adults",
state_parole_year()$state, state_parole_year()$number_on_parole_per_100000_us_adult_residents)})
output$mymap <- renderLeaflet({
state_map %>%
addTiles()%>%
addPolygons(fillColor = ~ pal(state_parole_year()$number_on_parole_per_100000_us_adult_residents),
fillOpacity = 1,
color = "blue",
opacity = 0.1,
weight = 1,
highlight = highlightOptions(
weight = 3,
color = "blue",
fillOpacity = .2,
bringToFront = TRUE),
label = labels_year())
})
}
When I run the leaflet map outside of r shiny app and change the year manually by subsetting the csv it works perfectly. The problem occurs when I try to make the labels reactive to the slider. Does someone know how I can fix the problem? Thanks!

Answer 1

The problem is that you build the map on unfiltered data, then display it with filtered data. There is then a switch in factors.
A quick fix is to build your map on filtered data, directly in the server() function :
output$mymap <- renderLeaflet({
leaflet(data = state_parole_year()) %>%
addTiles() %>%
setView(lng = -80,
lat = 34.5,
zoom = 4) %>%
addPolygons(fillColor = ~ pal(state_parole$number_on_parole_per_100000_us_adult_residents),
fillOpacity = 1,
color = "blue",
opacity = 0.1,
weight = 1,
highlight = highlightOptions(
weight = 3,
color = "blue",
fillOpacity = .2,
bringToFront = TRUE),
label = labels) %>%
addLegend(
position = "topright",
pal = pal,
values = ~number_on_parole_per_100000_us_adult_residents,
title = "# of U.S. Adults on Parole/100000.",
opacity = 1) %>%
addTiles()%>%
addPolygons(fillColor = ~ pal(state_parole_year()$number_on_parole_per_100000_us_adult_residents),
fillOpacity = 1,
color = "blue",
opacity = 0.1,
weight = 1,
highlight = highlightOptions(
weight = 3,
color = "blue",
fillOpacity = .2,
bringToFront = TRUE),
label = ~labels_year())
})