How to get last data for each id/date?

Question

I have a data frame that contains id, POSIXct(Date & Time)

> myData

   Tpt_ID    Tpt_DateTime               Value
1  1         2013-01-01 15:17:21 C         


        

Answer 1

Another data.table solution, which works in a manner similar to @SimonO101's answer -

library(data.table)
dt <- data.table( dt )
dt[ , Date:= as.Date( Tpt_DateTime ) ]

#indexing the data.table
setkey(dt,Tpt_ID,Date)
#mult = "last" returns te last row of each unique group as defined by the by argument
dt[dt[unique(dt), mult="last", which=TRUE]]

This returns -

> dt[dt[unique(dt),,mult="last", which=TRUE]]
   Tpt_ID        Tpt_DateTime Value       Date
1:      1 2013-01-01 16:47:21    21 2013-01-01
2:      1 2013-01-02 12:40:11    15 2013-01-02
3:      2 2013-01-01 12:48:32     5 2013-01-01
4:      2 2013-02-02 17:48:32     8 2013-02-02
5:      3 2013-01-01 13:30:02     1 2013-01-01
6:      3 2013-02-03 19:30:02     3 2013-02-03