在data.table中创建ITime间隔

Question

I have a datetime variable ( vardt ) as a character in large data table. Eg "21/07/2011 15:54:57"

I can turn it into ITime class (eg 15:54:57 ) with DT[,newtimevar:=as.ITime(substr(DT$vardt,12,19))] but I would like to create groups of minutes, so from 21/07/2011 15:54:57 I would obtain 15:54:00 or 15:54 .

I have tried: DT[,cuttime := as.ITime(cut(DT$vardt, breaks = "1 min",))] but it didn't work. I am reading the zoo package documentation but I haven't found anything yet. Any idea/function that could be useful for this case in a large data table?

Answer 1

Here are two possible approaches:

library(data.table)
##
x <- Sys.time()+sample(seq(0,24*3600,60),101,TRUE)
x <- gsub(
  "(\\d+)\\-(\\d+)\\-(\\d+)",
  "\\3/\\2/\\1",
  x)
##
DT <- data.table(vardt=x)
##
DT[,time:=as.ITime(substr(vardt,12,19))]
##
DT[,hour_min:=as.ITime(
  gsub("(\\d+)\\:(\\d+)\\:(\\d+)",
       "\\1\\:\\2\\:00",time))]
DT[,c_hour_min:=substr(time,1,5)]
##
R>  head(DT)
                 vardt     time hour_min c_hour_min
1: 28/01/2015 05:38:30 05:38:30 05:38:00      05:38
2: 27/01/2015 14:15:30 14:15:30 14:15:00      14:15
3: 28/01/2015 06:03:30 06:03:30 06:03:00      06:03
4: 28/01/2015 00:37:30 00:37:30 00:37:00      00:37
5: 27/01/2015 17:59:30 17:59:30 17:59:00      17:59
6: 28/01/2015 03:46:30 03:46:30 03:46:00      03:46
R>  str(DT,vec.len=2)
Classes ‘data.table’ and 'data.frame':  101 obs. of  4 variables:
 $ vardt     : chr  "28/01/2015 05:38:30" "27/01/2015 14:15:30" ...
 $ time      :Class 'ITime'  int [1:101] 20310 51330 21810 2250 64770 ...
 $ hour_min  :Class 'ITime'  int [1:101] 20280 51300 21780 2220 64740 ...
 $ c_hour_min: chr  "05:38" "14:15" ...
 - attr(*, ".internal.selfref")=<externalptr>

The first case, hour_min , preserves the ITime class, while the second case, c_hour_min , is just a character vector.