addSunTimes <- function(data)
{
require(chron)
if(length(data$sunrise) == 0 && length(data$sunset) == 0){
	data <- data.frame(data, sunrise = sunriseset(data$date, data$lat, data$lon, timez = 0)$sunrise/60, sunset = sunriseset(data$date, data$lat, data$lon, timez = 0)$sunset/60)
	}
if(length(data$day) == 0){
	data <- data.frame(data, day = ifelse((data$time < data$sunrise | data$time > data$sunset), 2, 1))
	}	
else {print(paste(deparse(substitute(data)), 'already contains sunrise/sunset times & day', sep = ' '))}
return(data)
}