changing data based of leaflet shiny input

Question

I would like to change data to plot on a shapefile (world) based on the year selected as input. According to you, which one is wiser:

1. Setting the data to wide (data_2020, data_2019, data_2018...) and change the column when the input changes ? -or-

2. Setting the data to long (data, year) and filter the data column based on year == 20XX when the input changes ?

I've been trying for days but couldn't manage to make it work. The example below is my server.R file where data has been set to long format and I selected one year in order to make reactivity work, but it doesn't update the data. The wide format does not work with the (commented) switch function.

function(input, output) {
  
  selectedYear <- reactive({
    #shape_data <- subset(shape_data, year == input$year)
    shape_data$month

    #datayear <- switch(input$year, 
    #       "2017" = shape_data$month2017, 
    #       "2018" = shape_data$month2018, 
    #       "2019" = shape_data$month2019)
  })
  
  
  output$mymap <- renderLeaflet({
    
    bins <- c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
    pal <- colorBin(c("#3EA055", "#FFE5B4", "#F2BB66", "#FFDB58", "#FBB117", "#C68E17", "#E56717", "#C34A2C", "#C11B17", "#9F000F", "#8C001A" , "#7E3517"), domain = selectedYear(), bins = bins, na.color = "#808080")
    
    leaflet(shape_data) %>%
    setView(0, 37.8, 2) %>%
    addTiles() %>% 
    addPolygons(fillColor = ~pal(selectedYear()),
                weight = 2,
                opacity = 1,
                color = "black",
                fillOpacity = 0.7)
   })
  
  observe({
    req(input$year)
      
    bins <- c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
    pal <- colorBin(c("#3EA055", "#FFE5B4", "#F2BB66", "#FFDB58", "#FBB117", "#C68E17", "#E56717", "#C34A2C", "#C11B17", "#9F000F", "#8C001A" , "#7E3517"), domain = selectedYear(), bins = bins, na.color = "#808080")
      
    leafletProxy("mymap", data = shape_data) %>%
      clearShapes() %>% 
      addPolygons(fillColor = ~pal(selectedYear()),
                  weight = 2,
                  opacity = 1,
                  color = "black",
                  fillOpacity = 0.7)
  })

Answer 1

Your statement

shape_data <- subset(shape_data, year == input$year)

changes shape_data after the first year selection. Please change it to

shape_data2 <- subset(shape_data, year == input$year)