To remind you of the server.R file, and to show you which bits we have retained, let's look at the server.R file first, shown in the following code:

library(tidyverse)
library(gapminder)

load("geocodedData.Rdata")

function(input, output) {
 
  theData = reactive({
 
    mapData %>%
      filter(year >= input$year[1])
  })
 
  output$trend = renderPlot({ 
 
  thePlot = theData() %>%
    group_by(continent, year) %>%
    summarise(meanLife = mean(lifeExp)) %>%
    ggplot(aes(x = year, y = meanLife, group = continent, 
      colour = continent)) + geom_line() + 
      ggtitle("Graph to show life expectancy by continent over time")
 
  if(input$linear){ 
    thePlot = thePlot + geom_smooth(method = "lm") 
  } 
 
  print(thePlot)
  })
}

There are no surprises in this code, really; it is just a cut-down version of the code from the previous chapter. You can see a reactive function to bring back the data (theData()), and a call to renderPlot(), which produces a line graph using ggplot().