add minutes to time of day (hh:mm), start from new day if time > 24

Question

I have a time variable as hh:mm. I want to add numeric minutes to that. If time goes over 24:00, it should count a new day.

For example: time starts at 23:45, delay is 20 minutes, real start time is 00:05. Example data frame:

df <- data.frame(time_start = c("23:45", "23:30", NA, "23:00", "00:30", "02:00"),
                 delay = c(20, 300, 10, 120, 5, 0)) # in minutes

This is my way to get minutes to a time format:

library(chron)
library(lubridate)
df$delay<- hms(times(df$delay/24))

But adding delay to time_start results in times > 24 hours. How can I start from a new day? Thanks in advance!

Answer 1

You could add a "neutral" date (e.g. "1970-01-01") to your time and format as.POSIXct. Then just add the delay (in seconds, therefore * 60). To finally display just the time, use format.

df <- transform(df, time_start2=as.POSIXct(
  ifelse(is.na(time_start), NA, paste(as.Date("1970-01-01"), time_start))
))

df$time_end <- format(with(df, time_start2 + delay * 60), "%H:%M")
df
# time_start delay         time_start2 time_end
# 1      23:45    20 1970-01-01 23:45:00    00:05
# 2      23:30   300 1970-01-01 23:30:00    04:30
# 3       <NA>    10                <NA>     <NA>
# 4      23:00   120 1970-01-01 23:00:00    01:00
# 5      00:30     5 1970-01-01 00:30:00    00:35
# 6      02:00     0 1970-01-01 02:00:00    02:00