Date-time differences between rows in R

Question

I would like to calculate time differences (delta time) in R. The timestamps are stored in a two-column data frame with time as date-time (year-month-day hour:min: sec.msec)

Answer 1

I will not give you the entire answer, but this will help you almost get there:

x="2012-07-11 04:22:40.169"
datex=strptime(x,format='%Y-%m-%d %H:%M:%S') #this converts your date string 
#into a date value recognized in r

y="2012-08-15 08:32:40.169"
datey=strptime(y,format='%Y-%m-%d %H:%M:%S')

time_diff=as.numeric(difftime(datey,datex)) #in decimal days
>35.17361

From decimal days you can then convert it back to whichever time format you want, but depending on what you want to do with it, you may want to keep it in a numeric form (perhaps in decimal hours, by multiplying time_diff by 24)...