'Create a time interval of 15 minutes from minutely data in R?

I have some data which is formatted in the following way: 

time     count 
00:00    17
00:01    62
00:02    41

So I have from 00:00 to 23:59hours and with a counter per minute. I'd like to group the data in intervals of 15 minutes such that:

time           count
00:00-00:15    148   
00:16-00:30    284

I have tried to do it manually but this is exhausting so I am sure there has to be a function or sth to do it easily but I haven't figured out yet how to do it.

I'd really appreciate some help!!

Thank you very much!

rtimeformat


Solution 1:[1]

The cut approach is handy but slow with large data frames. The following approach is approximately 1,000x faster than the cut approach (tested with 400k records.)

  #     Function: Truncate (floor) POSIXct to time interval (specified in seconds)
  #       Author: Stephen McDaniel @ PowerTrip Analytics
  #        Date : 2017MAY
  #    Copyright: (C) 2017 by Freakalytics, LLC
  #      License: MIT

  floor_datetime <- function(date_var, floor_seconds = 60, 
        origin = "1970-01-01") { # defaults to minute rounding
     if(!is(date_var, "POSIXct")) stop("Please pass in a POSIXct variable")
     if(is.na(date_var)) return(as.POSIXct(NA)) else {
        return(as.POSIXct(floor(as.numeric(date_var) / 
           (floor_seconds))*(floor_seconds), origin = origin))
     }
  }

Sample output:

test <- data.frame(good = as.POSIXct(Sys.time()), 
   bad1 = as.Date(Sys.time()),
   bad2 = as.POSIXct(NA))

test$good_15 <- floor_datetime(test$good, 15 * 60)
test$bad1_15 <- floor_datetime(test$bad1, 15 * 60)
Error in floor_datetime(test$bad, 15 * 60) : 
  Please pass in a POSIXct variable
test$bad2_15 <- floor_datetime(test$bad2, 15 * 60)

test

                        good       bad1 bad2             good_15 bad2_15
    1 2017-05-06 13:55:34.48 2017-05-06 <NA> 2007-05-06 13:45:00    <NA>

Solution 2:[2]

You can do it in one line by using trs function from FQOAT, just like:

df_15mins=trs(df, "15 mins")

Below is a repeatable example:

library(foqat)
head(aqi[,c(1,2)])
#            Time        NO
#1 2017-05-01 01:00:00 0.0376578
#2 2017-05-01 01:01:00 0.0341483
#3 2017-05-01 01:02:00 0.0310285
#4 2017-05-01 01:03:00 0.0357016
#5 2017-05-01 01:04:00 0.0337507
#6 2017-05-01 01:05:00 0.0238120

#mean
aqi_15mins=trs(aqi[,c(1,2)], "15 mins")
head(aqi_15mins)
#             Time         NO
#1 2017-05-01 01:00:00 0.02736549
#2 2017-05-01 01:15:00 0.03244958
#3 2017-05-01 01:30:00 0.03743626
#4 2017-05-01 01:45:00 0.02769419
#5 2017-05-01 02:00:00 0.02901817
#6 2017-05-01 02:15:00 0.03439455

Sources

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Source: Stack Overflow

Solution Source
Solution 1
Solution 2

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