Once again forgive my ignorance, but why can't whole column replacements using $ <- just redirect to ":="?
On 9 September 2011 12:42, Matthew Dowle <[email protected]> wrote: > Oops, I missed that the question was about whole column replacements. > > I'm generally using := now. Will have a think about this ... > > "Chris Neff" <[email protected]> wrote in message > news:caauy0ruusbcvsftyqbg4m+cwa3zhwrjmwpl-q0fblaq+egn...@mail.gmail.com... > This was surprising to me. I would've thought test.dt$X <- "foo" and > test.dt[["X"]] <- "foo" should do the exact same thing because the > entire column is being overwritten, no? I would understand the issue > if it was test.dt$X[i] <- "foo", but it isn't. > > In a related note, I'm surprised this doesn't work either: > >> DT=data.table(x=1:10,y=1:10,key="x") >> DT$x="foo" > Warning message: > In `[<-.data.table`(x, j = name, value = value) : > NAs introduced by coercion >> DT[["x"]]="foo" # Works fine and sets DT$x to be a character vector with >> "foo" repeated. > > DT$x is allowed to be overwritten by other classes (i.e. DT$x <- > rnorm(10) when DT$x starts as an integer), why not a character, or > change "foo" to a factor and assign it if that is what must be done? > This is also true with a non-key variable, like DT$y. > > > On 8 September 2011 18:15, Matthew Dowle <[email protected]> wrote: >> It's intended. data.table requires sorted factor levels. If the levels >> somehow become unsorted then binary search joins don't work. We might >> be able to allow it and make data.table maintain things (with a speed >> penalty due to the resort of levels and re-write of the entire integer >> column), but, allowing character columns is (hopefully) not far away >> which should be much better solution. >> >> Or, in the meantime, you can go 'under the hood'. Add "something >> different" to the end of the factor levels using levels()<-, then the >> assignment to the column should work. If that column is part of a key >> then make sure to recall setkey() which will check and resort the levels >> for you (with a warning message). If an existing level is changing name, >> then it's faster to assign (once) directly to the levels(). But again, >> careful to maintain sorted levels if that column is to be used in joins. >> >> Matthew >> >> >> On Thu, 2011-09-08 at 14:27 -0500, Damian Betebenner wrote: >>> Not sure whether the following is an intended behavior with >>> data.table. Perhaps it is something idiosyncratic with factors. >>> >>> It is different than what one gets with data.frame >>> >>> >>> >>> test.df <- data.frame(X=letters[1:10], Y=rnorm(10)) >>> >>> test.dt <- data.table(X=letters[1:10], Y=rnorm(10)) >>> >>> >>> >>> test.df$X <- "Something Different" >>> >>> test.dt$X <- "Something Different" >>> >>> Error in `[<-.data.table`(x, j = name, value = value) : >>> >>> Some or all RHS not present in factor column levels >>> >>> >>> >>> >>> >>> test.df <- data.frame(X=letters[1:10], Y=rnorm(10)) >>> >>> test.dt <- data.table(X=letters[1:10], Y=rnorm(10)) >>> >>> >>> >>> test.df[["X"]] <- "Something Different" >>> >>> test.dt[["X"]] <- "Something Different" >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> Damian Betebenner >>> >>> Center for Assessment >>> >>> PO Box 351 >>> >>> Dover, NH 03821-0351 >>> >>> >>> >>> Phone (office): (603) 516-7900 >>> >>> Phone (cell): (857) 234-2474 >>> >>> Fax: (603) 516-7910 >>> >>> >>> >>> [email protected] >>> >>> www.nciea.org >>> >>> >>> >>> >>> >>> >>> >>> >>> _______________________________________________ >>> datatable-help mailing list >>> [email protected] >>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help >> >> >> _______________________________________________ >> datatable-help mailing list >> [email protected] >> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help >> > > > > _______________________________________________ > datatable-help mailing list > [email protected] > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help > _______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
