You can use one of the following methods to subtract a certain number of hours from a time in R:

Method 1: Use Base R

#create new column that subtracts 4 hours from time
df$subtract4 <- df$time - (4*3600)

Method 2: Use lubridate Package

library(lubridate)

#create new column that subtracts 4 hours from time
df$subtract4 <- df$time - hours(4)

The following examples show how to use each method with the following data frame:

#create data frame
df <- data.frame(time=as.POSIXct(c('2022-01-03 08:04:15', '2022-01-05 14:04:15',
                                   '2022-01-05 20:03:53', '2022-01-06 03:29:13',
                                   '2022-01-06 06:15:00', '2022-01-07 10:48:11'),
                                   format='%Y-%m-%d %H:%M:%OS'),
                 sales=c(130, 98, 240, 244, 174, 193))

#view data frame
df

                 time sales
1 2022-01-03 08:04:15   130
2 2022-01-05 14:04:15    98
3 2022-01-05 20:03:53   240
4 2022-01-06 03:29:13   244
5 2022-01-06 06:15:00   174
6 2022-01-07 10:48:11   193

Note: To add hours to a date, simply change the subtraction sign to an addition sign in either of the formulas above.

Example 1: Subtract Hours from Time Using Base R

The following code shows how to create a new column called subtract4 that subtracts four hours from each value in the time column:

#create new column that subtracts 4 hours from time
df$subtract4 <- df$time - (4*3600)

#view updated data frame
df

                 time sales           subtract4
1 2022-01-03 08:04:15   130 2022-01-03 04:04:15
2 2022-01-05 14:04:15    98 2022-01-05 10:04:15
3 2022-01-05 20:03:53   240 2022-01-05 16:03:53
4 2022-01-06 03:29:13   244 2022-01-05 23:29:13
5 2022-01-06 06:15:00   174 2022-01-06 02:15:00
6 2022-01-07 10:48:11   193 2022-01-07 06:48:11

Notice that the values in the new subtract4 column are equal to the values in the time column with four hours subtracted from them.

Note: We use (4*3600) in the formula because time values are stored as seconds in R. Since there are 3,600 seconds in one hour, we must multiply 4 by 3,600 to subtract 4 hours.

Example 2: Subtract Hours from Time Using lubridate Package

The following code shows how to use the hours() function from the package to create a new column called subtract4 that subtracts four hours from each value in the time column:

library(lubridate)

#create new column that subtracts 4 hours from time
df$subtract4 <- df$time - hours(4)

#view updated data frame
df

                 time sales           subtract4
1 2022-01-03 08:04:15   130 2022-01-03 04:04:15
2 2022-01-05 14:04:15    98 2022-01-05 10:04:15
3 2022-01-05 20:03:53   240 2022-01-05 16:03:53
4 2022-01-06 03:29:13   244 2022-01-05 23:29:13
5 2022-01-06 06:15:00   174 2022-01-06 02:15:00
6 2022-01-07 10:48:11   193 2022-01-07 06:48:11

Notice that the values in the new subtract4 column are equal to the values in the time column with four hours subtracted from them.