Yes, sorry. Its nomatch= which presumably derives from the parameter of the same name in the match() function. If the idea of the nomatch= name was to leverage off existing argument names in R then I would prefer all.y= to be consistent with merge() in place of nomatch= since we are really merging/joining rather than just matching. That would also allow extension to all types of join by adding all.an x= argument too.
On Fri, May 3, 2013 at 10:59 AM, Eduard Antonyan <[email protected]> wrote: > I would prefer nomatch=0 as a default though, simply because that's what I > do most of the time :) > > > On Fri, May 3, 2013 at 9:57 AM, Eduard Antonyan <[email protected]> > wrote: >> >> A correction - the param is called "nomatch", not "match". >> >> This use case seems like smth a user shouldn't really do - in an ideal >> world you should have them both keyed by the same-name column. >> >> As is, my view on it is that data.table is correcting the user mistake of >> naming the column in Y - y, instead of x, and so the output makes sense and >> I don't see the need of complicating the behavior by adding more cases one >> has to go through to figure out what the output columns would be. Similar to >> asking for X[J(c("b", "c", "d"))] - you wouldn't want an anonymous column >> there, would you? >> >> >> >> On Fri, May 3, 2013 at 6:18 AM, Gabor Grothendieck >> <[email protected]> wrote: >>> >>> I am moving this discussion which started with mdowle to the list. >>> >>> Consider this example slightly modified from the data.table FAQ: >>> >>> > X = data.table(x=c("a","a","b","b","b","c","c"), foo=1:7, key="x") >>> > Y = data.table(y=c("b","c","d"), bar=c(4,2,3)) >>> > out <- X[Y]; out >>> x foo bar >>> 1: b 3 4 >>> 2: b 4 4 >>> 3: b 5 4 >>> 4: c 6 2 >>> 5: c 7 2 >>> 6: d NA 3 >>> >>> Note that the first column of the output is labelled x even though the >>> data to produce it comes from y, e.g. "d" in out$x is not in X$x but >>> does appear in Y$y so clearly the data is coming from y as opposed to >>> x . In terms of SQL the above would be written: >>> >>> select Y.y as x, ... >>> >>> and the need to renamne the first column of out suggests that there >>> may be a deeper problem here. >>> >>> Here are some ideas to address this (they would require changes to >>> data.table): >>> >>> - the default of X[Y,, match=NA] would be changed to a default of >>> X[Y,,match=0] so that it corresponds to the defaults in R's merge and >>> in SQL joins. >>> >>> - the column name of the first column in the example above would be >>> changed to y if match=0 but be left at x if match=NA. In the case >>> that match=0 (the proposed new default) x and y are equal so the first >>> column can be validly labelled as x but in the case that match=NA they >>> are not so y would be used as the column name. >>> >>> - the name match= does seem a bit misleading since R's match only >>> matches one item in the target whereas in data.table match matches >>> many if mult="all" and that is the default. Perhaps some thought >>> should be given to a name change here? >>> >>> The above would seem to correspond more closely to R's merge and SQL >>> join defaults. Any use cases or other comments? >>> >>> -- >>> Statistics & Software Consulting >>> GKX Group, GKX Associates Inc. >>> tel: 1-877-GKX-GROUP >>> email: ggrothendieck at gmail.com >>> _______________________________________________ >>> datatable-help mailing list >>> [email protected] >>> >>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help >> >> > -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com _______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
