Matthew, > How about ~ instead of ! ? I ruled out - previously to leave + and - > available for future use. NJ() may be possible too. Both "NJ()" and "~" are okay for me.
> That result makes perfect sense to me. I don't think of !(x==.) being the > same as x!=. ! is simply a prefix. It's all the rows that aren't > returned if the ! prefix wasn't there. > > > I understand that `DT[!(x)]` does what `data.table` is designed to do currently. What I failed to mention was that if one were to consider implementing `!(x==.)` as the same as `x != .` then this behaviour has to be changed. Let's forget this point for a moment. > That needs to be fixed. But we're getting quite theoretical here and far > away from common use cases. Why would we ever have row numbers of the table, > as a column of the table itself and want to select the rows by number not > mentioned in that column? Probably I did not choose a good example. Suppose that I've a data.table and I want to get all rows where "x == 0". Let's say: set.seed(45) DT <- data.table( x = sample(c(0,5,10,15), 10, replace=TRUE), y = sample(15)) DF <- as.data.frame(DT) To get all rows where x == 0, it could be done with DT[x == 0]. But it makes sense, at least in the context of data.frames, to do equivalently, DF[!(DF$x), ] (or) DF[DF$x == 0, ] All I want to say is, I expect `DT[!(x)]` should give the same result as `DT[x == 0]` (even though I fully understand it's not the intended behaviour of data.table), as it's more intuitive and less confusing. So, changing `!` to `~` or `NJ` is one half of the issue for me. The other is to replace the actual function of `!` in all contexts. I hope I came across with what I wanted to say, better this time. Best, Arun On Monday, June 10, 2013 at 10:52 AM, Matthew Dowle wrote: > > Hi, > How about ~ instead of ! ? I ruled out - previously to leave + and - > available for future use. NJ() may be possible too. > Matthew > > On 10.06.2013 09:35, Arunkumar Srinivasan wrote: > > Hi Matthew, > > My view (from the last reply) more or less reflects mnel's comments here: > > http://stackoverflow.com/questions/16239153/dtx-and-dtx-treat-na-in-x-inconsistently#comment23317096_16240143 > > > > Pasted here for convenience: > > data.table is mimicing subset in its handling of NA values in logical i > > arguments. -- the only issue is the ! prefix signifying a not-join, not the > > way one might expect. Perhaps the not join prefix could have been NJ not ! > > to avoid this confusion -- this might be another discussion to have on the > > mailing list -- (I think it is a discussion worth having) > > > > Arun > > > > On Monday, June 10, 2013 at 10:28 AM, Arunkumar Srinivasan wrote: > > > > > > Hm, good point. Is data.table consistent with SQL already, for both == > > > > and !=, and so no change needed? > > > > > > > > > > > > > > Yes, I believe it's already consistent with SQL. However, the current > > > interpretation of NA (documentation) being treated as FALSE is not needed > > > / untrue, imho (Please see below). > > > > > > > And it was correct for Frank to be mistaken. > > > > > > > > > > > > > > Yes, it seems like he was mistaken. > > > > Maybe just some more documentation and examples needed then. > > > > > > > > > > > > > > It'd be much more appropriate if the documentation reflects the role of > > > subsetting in data.table mimicking "subset" function (in order to be in > > > line with SQL) by dropping NA evaluated logicals. From a couple of posts > > > before, where I pasted the code where NAs are replaced to FALSE were not > > > necessary as `irows <- which(i)` makes clear that `which` is being used > > > to get indices and then subset, this fits perfectly well with the > > > interpretation of NA in data.table. > > > > Are you happy that DT[!(x==.)] and DT[x!=.] do treat NA inconsistently? > > > > : > > > > http://stackoverflow.com/questions/16239153/dtx-and-dtx-treat-na-in-x-inconsistently > > > > > > > > > > > > > > Ha, I like the idea behind the use of () in evaluating expressions. It's > > > another nice layer towards simplicity in data.table. But I still think > > > there should not be an inconsistency in equivalent logical operations to > > > provide different results. If !(x== .) and x != . are indeed different, > > > then I'd suppose replacing `!` with a more appropriate name as it's much > > > easier to get confused otherwise. > > > In essence, either !(x == .) must evaluate to (x != .) if the underlying > > > meaning of these are the same, or the `!` in `!(x==.)` must be replaced > > > to something that's more appropriate for what it's supposed to be. > > > Personally, I prefer the former. It would greatly tighten the structure > > > and consistency. > > > > "na.rm = TRUE/FALSE" sounds good to me. I'd only considered nomatch > > > > before in the context of joins, not logical subsets. > > > > > > > > > > > > > > Yes, I find this option would give more control in evaluating expressions > > > with ease in `i`, by providing both "subset" (default) and the typical > > > data.frame subsetting (na.rm = FALSE). > > > Best regards, > > > > > > Arun > > > > > > > > > > > > > > > > > >
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