The server part of my error-tracking Shiny app.

server.R

library(shiny)

# Load the data from our CSV file
logfreq <- read.csv('portalserr.csv')
logfreq$date <- as.POSIXct(logfreq$date)
# Calculate error rate per thousand accesses
logfreq$perthou <- logfreq$error.count / logfreq$access.count * 10^3

shinyServer(function(input, output) {
  output$freqPlot <- renderPlot({
    if (is.null(input$errors_shown)) {
      # If no checkboxes are checked, dislay an empty plot.
      print(ggplot(data.frame(x=c(0),y=c(0))) + geom_point(aes(x,y), alpha=0))
    } else {
      lf.filtered <- subset(logfreq, error.id %in% input$errors_shown)

      p <- ggplot(lf.filtered) +
        geom_point(aes(date, perthou, color=error.id), size=3) +
        geom_line(aes(date, perthou, color=error.id, group=error.id), size=2) +
        expand_limits(ymin=0) +
        theme(legend.position='left') +
        ggtitle('Errors per thousand requests') +
        ylab('Errors per thousand requests') +
        xlab('Date')
      print(p)
    }
  })
})