[datatable-help] IDate somehow gets converted to numeric?

[Chris Neff]

This was kind of hard to track down. An example:

> DT <- data.table(date=as.IDate(rep("2010-01-01",10)),x=1:10)

> DT <- as.data.frame(DT)

> str(DT)
'data.frame':   10 obs. of  2 variables:
 $ date:Classes 'IDate', 'Date'  int [1:10] 14610 14610 14610 14610
14610 14610 14610 14610 14610 14610
 $ x   : int  1 2 3 4 5 6 7 8 9 10

> DT2 <- ddply(DT, c("date", "x"), identity)

> str(DT2)
'data.frame':   10 obs. of  2 variables:
 $ date:Classes 'IDate', 'Date'  num [1:10] 14610 14610 14610 14610 14610 ...
 $ x   : int  1 2 3 4 5 6 7 8 9 10


As you can see int has changed to num here. If I try to convert back
to a data table and key on date again:

> DT2 <- as.data.table(DT2)
> key(DT2)="date"
Error in setkey("x", value) :
  Column 'date' cannot be auto converted to integer without losing information.

Whereas converting DT back to a data table and keying on date works fine.  Bug?

-Chris