Re: [Rd] setdiff bizarre

From: William Dunlap <>
Date: Tue, 02 Jun 2009 11:29:03 -0700

> > ...
> > The related functions, duplicated() and unique(), do have
> > row-wise data.frame methods. E.g.,
> > > duplicated(data.frame(x=c(1,2,2,3,3),y=letters[c(1,1,2,2,2)]))
> > Perhaps match() ought to have one also. S+'s match is generic
> > and has a data.frame method (which is row-oriented) so there we get:
> > > match(data.frame(x=c(1,3,5), y=letters[c(1,3,5)]),
> > data.frame(x=1:10,y=letters[1:10]))
> > [1] 1 3 5
> > > is.element(data.frame(x=1:10,y=letters[1:10]),
> > data.frame(x=c(1,3,5), y=letters[c(1,3,5)]))
> >
> > I think that %in% and is.element() ought to remain calls to match()
> > and that if you want them to work row-wise on data.frames then
> > match should get a data.frame method.

> >

> sounds good to me.  how is
>     'a' %in% data.frame('a')
> in S+?
> thanks for the response.

S+ gives:

   > 'a' %in% data.frame(letters)
   [1] TRUE
   > 'a' %in% data.frame(letters[2:26])
   [1] FALSE
but that special case, x a scalar and table a data.frame with one column, gets by more or less by accident.

   > 'a' %in% data.frame(letters, num=1:26)    Problem in, table, nomatch, incom..: table must be a list the same length as x

   > c('a', 'b') %in% data.frame(letters)    Problem in, table, nomatch, incom..: table must be a list the same length as x
The intent is that the x and table arguments to match be compatible data.frames.

S+'s match works differently on lists than R's does. It is set up to work on data.frame-like things: x and table must be lists of the the same length and within each list, each element must have the same length. It acts like   match("paste",x),"paste",table)) but doesn't actually do the conversion to character implied in that (it hashes all the entries in each 'row' into one hash table entry, using the usual type-specific hash number computation on each entry and combining them to make the row hash number). E.g.,

   > match(list(c(3,2), c(1,7), c(4,1)), list(c(1,4,2,3),c(0,6,7,1),c(0,5,1,4)))

   [1] 4 3

(Its doesn't actually call this, for historical/inertial
reasons. It goes the paste() route.)  

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap mailing list Received on Tue 02 Jun 2009 - 18:39:08 GMT

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