Why does this POSIXct or ITime loses its format/attribute
data.table, r
Solution
Update: This has been fixed in v1.8.11. From NEWS:
`:=` (assignment by reference) loses `POSIXct` or `ITime` attribute while grouping is now fixed, #2531. Tests added. Thanks to stat quant for reporting here: Why does this POSIXct or ITime loses its format/attribute and to Paul Murray for reporting here on SO: Cannot assign columns as.Date by reference in data.table
Please write back if I seem to have overlooked something.
Problem
here is my sample data, I do not understand why the `ITime` column loses it's format in the following code using the `data.table` package ``` DT = data.table(x=as.POSIXct(c("2009-02-17 17:29:23.042", "2009-02-17 17:29:25.160")), y=c(1L,2L)) DT[,x1:=as.ITime(x)] DT[,`:=`(last.x=tail(x,1L),last.x1=tail(x1,1L)),by=y] DT x y x1 last.x last.x1 1: 2009-02-17 17:29:23.042 1 17:29:23 1234888163 62963 2: 2009-02-17 17:29:25.160 2 17:29:25 1234888165 62965 ``` But If `data.table` already knows the format like in the following, It works ``` DT = data.table(x=as.POSIXct(c("2009-02-17 17:29:23.042", "2009-02-17 17:29:25.160")), y=c(1L,2L)) DT[,x1:=as.ITime(x)] DT[,`:=`(last.x=x,last.x1=x1)] #HERE DATA>TABLE KNOWS THE LAST.* FORMAT DT[,`:=`(last.x=tail(x,1L),last.x1=tail(x1,1L)),by=y] R) DT x y x1 last.x last.x1 1: 2009-02-17 17:29:23.042 1 17:29:23 2009-02-17 17:29:23.042 17:29:23 2: 2009-02-17 17:29:25.160 2 17:29:25 2009-02-17 17:29:25.160 17:29:25 ``` It must be something about how `data.table` assigns, is there a work around ? UPDATE Thanks to Arun this is now fixed ``` R) library(data.table) data.table 1.8.11 For help type: help("data.table") R) DT = data.table(x=as.POSIXct(c("2009-02-17 17:29:23.042", + "2009-02-17 17:29:25.160")), + y=c(1L,2L)) R) DT[,x1:=as.ITime(x)] R) DT[,`:=`(last.x=tail(x,1L),last.x1=tail(x1,1L)),by=y] R) DT x y x1 last.x last.x1 1: 2009-02-17 17:29:23.042 1 17:29:23 2009-02-17 17:29:23.042 17:29:23 2: 2009-02-17 17:29:25.160 2 17:29:25 2009-02-17 17:29:25.160 17:29:25 ```