Allow ggplot2 to handle forecast result

fortify_forecast.R

library(forecast)
library(ggplot2)

d <- AirPassengers
d.arima <- forecast::auto.arima(d)
d.forecast <- forecast(d.arima, level = c(95), h = 50)

fortify.forecast <- function(forecast.data) {
  require(dplyr)
  forecasted <- as.data.frame(forecast.data)
  forecasted$Time <- as.Date(time(forecast.data$mean))
  
  fitted <- data.frame(Time = as.Date(time(forecast.data$fitted)),
                       Original = forecast.data$x,
                       Fitted = forecast.data$fitted)

  rownames(fitted) <- NULL
  rownames(forecasted) <- NULL

  dplyr::rbind_list(fitted, forecasted)
}

head(ggplot2::fortify(d.forecast))

ggplot(data = d.forecast) +
  geom_line(mapping = aes_string(x = 'Time', y = 'Original')) +
  geom_line(mapping = aes_string(x = 'Time', y = '`Point Forecast`'), colour='blue') +
  geom_ribbon(mapping = aes_string(x = 'Time', ymin = '`Lo 95`', ymax = '`Hi 95`'), alpha = 0.5)