+1; I especially like #2 and the slight conceptual shift it implies
On Sat, May 4, 2013 at 6:26 AM, Gabor Grothendieck <[email protected]>wrote: > The proposal at this point would be: > > 1. nomatch= would be replaced by all.i= such that > X[Y,,nomatch=NA] is the same as X[Y,,all.i=TRUE] > X[Y,,nomatch=0] is the same as X[Y,,all.i=FALSE] > nomatch= would be deprecated and ultimately removed. > > Note that #1 is simple to implement as it only involves changing names > and values of arguments and does not really change any behavior; > however, its easier to think about because X[Y,,all.i=Z] now has the > same behavior as merge(X, Y, all.y=Z) and so can be quickly understood > by anyone who knows merge in R. In contrast nomatch= did not even > have the same meaning as in match() since match matches the first > occurrence whereas with mult="all", the default, matching in > data.table matches all occurrences. Note that the default of merge's > all.y= is all.y=FALSE but the default of all.i= is all.i=TRUE in order > that the default behave as indices do. Also note that this solves the > problem that nomatch= can only be 0 or NA since a logical can only > have two non-NA values anyways. > > 2. If Y were a numeric index vector then all.i= will have the same > effect as if Y were a data.table with Y as its column and is merged > with the row numbers of X. e.g. X[1:4,,all.i=FALSE] would be the > same as X[1:3] if X only had 3 rows since 4 does not match a row > number of X and is dropped because all.i=FALSE. If Y were a numeric > vector with negative values it would be converted to one with positive > values in such a way as to have the established meaning and then the > same strategy is applied. If Y were logical then its recycled giving > YY and the same strategy is applied to which(YY). This description is > intended to be conceptual and the actual internal mechanism could be > different. > > Thus #2 allows one to think of **all** i indexing as merging rather > than as multiple separate concepts (which I believe is consistent with > the original intention of data.table). > > > > > > > On Fri, May 3, 2013 at 8:02 PM, Eduard Antonyan > <[email protected]> wrote: > > I think I like this proposal - maybe you should write up a few examples > of > > what current behavior is, vs the proposed behavior. > > > > > > On Fri, May 3, 2013 at 6:54 PM, Gabor Grothendieck < > [email protected]> > > wrote: > >> > >> data.table is supposed to generalize indexing and although not > >> explicitly stated the generalization seems to be that indexing is > >> merging with the row numbers so there is indeed merging going on and > >> that merging should respect nomatch= for consistency. > >> > >> On Fri, May 3, 2013 at 6:54 PM, Eduard Antonyan > >> <[email protected]> wrote: > >> > There is no join'ing happening here, thus nomatch=0 has no effect. > >> > > >> > > >> > On Fri, May 3, 2013 at 5:52 PM, Gabor Grothendieck > >> > <[email protected]> > >> > wrote: > >> >> > >> >> The definition of DT was left out by mistake. It should be: > >> >> > >> >> DT <- data.table(a=letters[1:3]) > >> >> > >> >> > >> >> On Fri, May 3, 2013 at 6:50 PM, Gabor Grothendieck > >> >> <[email protected]> wrote: > >> >> > Consider this example: > >> >> > > >> >> >> DT[1:4,,nomatch=0] > >> >> > a > >> >> > 1: a > >> >> > 2: b > >> >> > 3: c > >> >> > 4: NA > >> >> > > >> >> > Should it not return only the first 3 rows? It seems to be > ignoring > >> >> > the nomatch=0. > >> >> > > >> >> > -- > >> >> > Statistics & Software Consulting > >> >> > GKX Group, GKX Associates Inc. > >> >> > tel: 1-877-GKX-GROUP > >> >> > email: ggrothendieck at gmail.com > >> >> > >> >> > >> >> > >> >> -- > >> >> 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 > > > > > > > > -- > Statistics & Software Consulting > GKX Group, GKX Associates Inc. > tel: 1-877-GKX-GROUP > email: ggrothendieck at gmail.com >
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