How to find the difference between two rows of data consisting of date and time in R -


i working data file consisting of 1 column of date , time 

df     time_stamp 1 2003-09-06t20:21:51z  (2003-09-06--> year-month-days-hours-mintutes-seconds) 2 2003-09-06t20:22:36z 3 2003-09-06t20:22:51z 4 2003-09-06t20:23:06z 5 2003-09-06t20:24:56z 6 2003-09-06t20:25:06z

i want find difference between 2 rows based on unit of minutes. have applied code 1st convert data date format, gives me error like:

 x<-as.date(df,format='%d/%b/%y:%h:%m:%s')  error in as.date.default(datew, format = "%d/%b/%y:%h:%m:%s") :    not know how convert 'datew' class “date”

while mode(df) shows results of "list"

any highly appreciated. output should as:

 df     time_stamp                   time_duration 1 2003-09-06t20:21:51z              0 2 2003-09-06t20:22:36z              1 3 2003-09-06t20:22:51z              0.25   4 2003-09-06t20:23:06z              0.25 5 2003-09-06t20:24:56z              1.8 6 2003-09-06t20:25:06z              0.17

thanks, in advance.

you seem passing list as.date function, , doesn't know how deal lists. try following.

first create data 

time_stamp <-  c(  "2003-09-06t20:21:51z",               "2003-09-06t20:22:36z",               "2003-09-06t20:22:51z",               "2003-09-06t20:23:06z",               "2003-09-06t20:24:56z",               "2003-09-06t20:25:06z")  df <- list(time_stamp=time_stamp)

now turn posix date. note format="%y-%m-%dt%h:%m:%sz" argument differs yours, since yours produced error when tried it. format has reflect nature of date string. see help(strptime) details.

x<-as.posixct(df$time_stamp,format="%y-%m-%dt%h:%m:%sz" , tz="gmt")  # comparison @akrun suggested time_duration <- difftime(x[-1], x[-length(x)], unit='mins') # add 0 start  time_duration <- c(0 , time_duration)  # make dataframe df <- data.frame( time_stamp=df$time_stamp , time_duration=time_duration )

and result wanted:

> df             time_stamp time_duration 1 2003-09-06t20:21:51z     0.0000000 2 2003-09-06t20:22:36z     0.7500000 3 2003-09-06t20:22:51z     0.2500000 4 2003-09-06t20:23:06z     0.2500000 5 2003-09-06t20:24:56z     1.8333333 6 2003-09-06t20:25:06z     0.1666667

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