Error in UseMethod: no applicable method for 'metaData' applied to an object of class "NULL"

library(shiny)
library(shinydashboard)
library(leaflet)
library(plotly)
library(RColorBrewer)
library(readxl)

# Load data
d1 <- read_excel("/path/Desktop/milk.xlsx", sheet ="Data")

# Define UI for dashboard
ui <- dashboardPage(
  # Application title
  dashboardHeader(title = "Milk Buddy"),
  
  # Sidebar menu
  dashboardSidebar(
    sidebarMenu(
      # About page
      menuItem("About", tabName = "about", icon = icon("info-circle")),
      # Map page
      menuItem("Map", tabName = "map", icon = icon("globe"))
    )
  ),
  
  # Application body
  dashboardBody(
    # Tab panels
    tabItems(
      # About page
      tabItem(tabName = "about",
              # Box to display about information
              box(width = 12, status = "primary", solidHeader = TRUE, title = "About Milk Buddy", 
                  textOutput("about_text")),
      ),
      # Map page
      tabItem(tabName = "map",
              # Box to display map
              box(width = 8, status = "primary", solidHeader = TRUE, title = "Milk Shortage Map", 
                  leafletOutput("map")),
              # Box to display input widgets
              box(width = 4, status = "primary", solidHeader = TRUE, title = "Input", 
                  selectInput("county", "County", choices = unique(d1$County), multiple = TRUE, selected = unique(d1$County)),
                  selectInput("month", "Month", choices = unique(d1$Month), multiple = TRUE, selected = unique(d1$Month)),
                  selectInput("shortfall", "Shortfall/No Shortfall", choices = c("Shortfall", "No Shortfall", "All"), selected = "All"),
                  plotlyOutput("waterfall")
              )
      )
    )
  )
)

# Define server logic
server <- function(input, output) {
  # About text output
  output$about_text <- renderText({
    paste("The Milk Buddy app predicts monthly milk shortage by county 
          and provides an interactive map and data table for visualization 
          and download. By examining the relationship between Wisconsin's 
          milk production, maximum Wisconsin temperatures, and the distribution 
          operations of Feeding America Eastern Wisconsin (FAEW), this analysis 
          aims to uncover insights for FAEW food procurement and operations teams. 
          The app will inform strategies to optimize resource allocation, improve 
          equitable distribution, and minimize milk wastage.")
  })
  
  # Create map
  output$map <- renderLeaflet({
    # Filter data based on user input
    filtered_data <- d1 %>%
      filter(!is.na(MonthlyShortfall), MonthlyShortfall > 0, County %in% input$county, Month %in% input$month) %>%
      filter(if (input$shortfall == "Shortfall") MonthlyShortfall > 0 else if (input$shortfall == "No Shortfall") MonthlyShortfall <= 0 else TRUE)
    
    # Use req() to check if filtered_data is not empty
    req(nrow(filtered_data) > 0)
    
    # Create map object
    map <- leaflet() %>%
      # Set view to Wisconsin
      setView(lng = -89.6414, lat = 43.7534, zoom = 6) %>%
      # Add base map tiles
      addTiles() %>%
      # Add markers for each county
      addCircleMarkers(
        data = filtered_data,
        lng = ~Longitude,
        lat = ~Latitude,
        radius = ~sqrt(MonthlyShortfall/1000),
        color = ~colorRampPalette(c("red", "yellow", "blue"))(100)[MonthlyShortfall/max(MonthlyShortfall)],
        stroke = FALSE,
        fillOpacity = 0.7,
        popup = ~paste("County: ", County, "<br>",
                       "Monthly Shortfall: ", MonthlyShortfall, "gallons")
      ) 
    
    # Add legend
    map <- map %>%
      addLegend(
        position = "bottomright",
        pal = palette("RdYlBu"),
        values = ~MonthlyShortfall,
        title = "Monthly Milk Shortfall",
        labFormat = labelFormat(transform = function(x) x/1000, suffix = " thousand gallons")
      )
    
    return(map)
  })
  
  # Create waterfall chart
  output$waterfall <- renderPlotly({
    filtered_data <- d1 %>%
      filter(!is.na(MonthlyShortfall), MonthlyShortfall > 0, County %in% input$county, Month %in% input$month) %>%
      filter(if (input$shortfall == "Shortfall") MonthlyShortfall > 0 else if (input$shortfall == "No Shortfall") MonthlyShortfall <= 0 else TRUE)
    
    # Calculate percentages for each QPR group
    filtered_data <- filtered_data %>%
      group_by(County, Month) %>%
      mutate(TotalWeight = sum(QPR_Group_Weight),
             Percentage = QPR_Group_Weight/TotalWeight*100)
    
    if (nrow(filtered_data) > 0) {
      chart <- plot_ly(data = filtered_data, x = ~County, y = ~Percentage, type = "bar",
                       color = ~QPR.Group, colors = c("green", "blue", "red"),
                       text = ~paste(QPR.Group, ": ", Percentage, "%"),
                       hovertemplate = paste("%{x}<br>%{y}%<extra></extra>")) %>%
        layout(title = "Milk Source Distribution",
               xaxis = list(title = "County"),
               yaxis = list(title = "Percentage"),
               barmode = "stack")
    } else {
      chart <- plot_ly() %>%
        layout(title = "Milk Source Distribution",
               xaxis = list(title = "County"),
               yaxis = list(title = "Percentage"),
               barmode = "stack")
    }
    return(chart)
  })
  
  # Create popup for map
  observeEvent(input$map_shape_click, {
    if (!is.null(input$map_shape_click)) {
      # Get county name and month from clicked marker
      county <- input$map_shape_click$properties$County
      month <- input$map_shape_click$properties$Month
      
      # Filter data for clicked county and month
      filtered_data <- d1 %>%
        filter(County == county, Month == month)
      
      # Calculate percentages for each QPR group
      filtered_data <- filtered_data %>%
        group_by(County, Month) %>%
        mutate(TotalWeight = sum(QPR_Group_Weight),
               Percentage = QPR_Group_Weight/TotalWeight*100)
      
      # Create popup content
      popup_content <- paste("County: ", county, "<br>",
                             "Rank: ", min(rank(filtered_data$MonthlyShortfall)),
                             "<br>",
                             "Milk Source Distribution:",
                             "<br>",
                             "1-Donated: ", round(sum(filtered_data$Percentage[filtered_data$QPR.Group == "1-Donated"]), 2), "%",
                             "<br>",
                             "2-Purchased: ", round(sum(filtered_data$Percentage[filtered_data$QPR.Group == "2-Purchased"]), 2), "%",
                             "<br>",
                             "3-Federal-USD: ", round(sum(filtered_data$Percentage[filtered_data$QPR.Group == "3-Federal-USD"]), 2), "%",
                             "<br>",
                             "Max Temp: ", max(filtered_data$MaxTemp))
      
      # Update popup for clicked marker
      leafletProxy("map") %>%
        clearPopups() %>%
        addPopups(input$map_shape_click$lng, input$map_shape_click$lat, popup_content)
    }
  })
}

# Run the application 
shinyApp(ui = ui, server = server)

Hi everyone, I'm creating an app, everything works except the map. When I run the app, it kept saying Error in UseMethod: no applicable method for 'metaData' applied to an object of class "NULL". Could someone help me? I would really appreciate it!!

Hi @Jiaqi_Wang , i would help but i would need the milk.xlsx or a simpler version of your app to reproduce your error first.

@Jiaqi_Wang Did you find the error? Because I been spending my last 3 hours of today looking for NA or NULL that doesn't exist.

My map with regular markers works fine, but when I try to add categories into it. I get the NULL or NA error:

 deck_lf_cic <- leaflet() %>%
+    setView(lng = mean(c(bbox_dioc["xmin"], bbox_dioc["xmax"])),
+            lat = mean(c(bbox_dioc["ymin"], bbox_dioc["ymax"])), zoom = 6) %>%
+    addProviderTiles("OpenStreetMap.Mapnik", group = "Mapnik") %>%
+    addPolygons(data = dioc,
+                color = "#b2aeae",
+                fillOpacity = 0,
+                weight = 1,
+                smoothFactor = 0.6) %>%
+    #addMarkers(lng = cic_sf$DisplayX, lat = cic_sf$DisplayY, popup = popup_cic, icon = report_tec_icon, group = "Parishes", clusterOptions = markerClusterOptions()) %>%
+    addMarkers(lng = cic_sf$DisplayX, lat = cic_sf$DisplayY, popup = popup_cic, icon = ~icons[pal(risk_level_all)], clusterOptions = markerClusterOptions()) %>%
+    addLegend(pal = pal, values = cic$risk_level_all, position = "bottomright") %>%
+    setMaxBounds(lng1 = bbox_dioc["xmin"] - 2,
+                 lat1 = bbox_dioc["ymin"] - 2,
+                 lng2 = bbox_dioc["xmax"] + 2,
+                 lat2 = bbox_dioc["ymax"] + 2)
Error in UseMethod("metaData") : 
  no applicable method for 'metaData' applied to an object of class "NULL"

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