difftime in R is not calculating correctly

Question

I am trying to find the difference between two dates in hours, and for the time differences that occur over the span of more than one day I am getting really outrageous and incorrect numbers.

Here is an example of the data:

     Observation    Status       DateTime                                
     1               Active     2016-11-04 22:32:49                 
     2              Inactive    2016-11-05 08:30:56   

I am running this command:

      getDiff <- function(x) {
      difftime(shift(x, fill = NA, type = "lead"), x, units = "hours")
       }

   diff_result <- dataframe[, time.diff := ifelse(Status == "Active", 
                                         getDiff(DateTime), NA)]

And I get the following output:

   Observation    Status       DateTime                   Time.diff             
   1               Active     2016-11-04 22:32:49       8757.884          
   2              Inactive    2016-11-05 08:30:56   

This command works for all other differences that do not happen on separate days. The correct answer should be around 10 hours, not over 8000.

Also,

    > class(DataFrame$DateTime)
   [1] "POSIXct" "POSIXt"

Thank you in advance!

Answer 1

It seems OP has not converted DateTime format correctly. The 8757 hours are equivalent to about 1 year. Hence, it is possible DateTime are wrongly formatted.

The result looks fine using OP's data at my end.

library(data.table)

getDiff <- function(x) {
  difftime(shift(x, fill = NA, type = "lead"), x, units = "hours")
}
setDT(df)
diff_result <- df[, time.diff := ifelse(Status == "Active", 
                                               getDiff(DateTime), NA)]


diff_result
#    Observation   Status            DateTime time.diff
# 1:           1   Active 2016-11-04 22:32:49  9.968611
# 2:           2 Inactive 2016-11-05 08:30:56        NA
# 

Data:

df <- read.table(text = 
"Observation    Status       DateTime                                
1               Active     '2016-11-04 22:32:49'                 
2              Inactive    '2016-11-05 08:30:56'",
header = TRUE, stringsAsFactors = FALSE)

df$DateTime = as.POSIXct(df$DateTime, format = "%Y-%m-%d %H:%M:%S")