overnight_temps.R

#'  overnight_temps.R
#'  https://twitter.com/AbsLawson/status/777799977393270784
#'
#'  rstats q: want to calc overnight temp (~22:00-4:00) from hrly temps w/ missing
#'  values (rows). Desired timespan overlaps dates, unsure how

# Create dummy data to use
df <- data.frame(datetime = seq(ISOdate(2016,1,1), ISOdate(2016,3,1), by = "hour"))
df$temp_c <- runif(nrow(df), 0, 20)

#' Calculate day of year and hour of day
#'
#' I always try to work in 'ordinal' dates and times because comparing dates
#' seems to be so finicky
df$day_of_year <- as.numeric(format(df$datetime, "%j"))
df$hour_of_day <- as.numeric(format(df$datetime, "%H"))

#' Here I Calculate "daily means" where daily is your definition of 2200 to 0400
#' the next day. I use an lapply() here but you could also do a for loop.
lapply(unique(df$day_of_year), function(day) {
  mean(df[(df$day_of_year == day & df$hour_of_day >= 22) | (df$day_of_year == (day + 1) & df$hour_of_day <= 4),"temp_c"])
})