There is a bug in identical(), though:
> identical(pairlist(a=1, b=2), pairlist(a=1, aa=2))
[1] TRUE
> identical(structure(pi, a=1, b=2), structure(pi,a=1, aa=2))
[1] TRUE
so identical() is not even looking at the names of the attributes but only
checking their values. Oops ....
On Fri, 1 Sep 2006, Prof Brian Ripley wrote:
> Please point us to the documentation that says attributes are ordered.
> E.g. R-lang.texi says
>
> All objects except @code{NULL} can have one or more attributes attached
> to them. Attributes are stored as a list where all elements are named.
>
> (although in fact they are stored in a pairlist).
>
> I know of tens of functions that change the order of attributes, and
> did look at teaching identical() that they are not ordered. But
> since they are stored as a pairlist, it would be quite expensive.
> (Given that attributes seem to be growing in use, another internal storage
> mechanism is becoming more appropriate.)
>
> BTW, all.equal() does not assume attributes are ordered.
>
>
> On Fri, 1 Sep 2006, [EMAIL PROTECTED] wrote:
>
> > This is a multi-part message in MIME format.
> > --------------090203020600020104020707
> > Content-Type: text/plain; charset=UTF-8
> > Content-Transfer-Encoding: 7bit
> >
> > Hello!
> >
> > I was doing some tests with identical() and found out that [<-.POSIXlt
> > method changes order of attributes. This example shows that:
> >
> > x <- strptime("1900-1-1", format="%Y-%m-%d")
> > x <- c(x)
> > y <- c(x, x+1)
> > x1 <- x
> > y1 <- y
> >
> > attributes(x)
> > $names
> > [1] "sec" "min" "hour" "mday" "mon" "year" "wday" "yday" "isdst"
> >
> > $class
> > [1] "POSIXt" "POSIXlt"
> >
> > $tzone
> > [1] "" "CET" "CEST"
> >
> > identical(attributes(x), attributes(y))
> > TRUE
> >
> > x[1] <- NA
> > attributes(x)
> > $names
> > [1] "sec" "min" "hour" "mday" "mon" "year" "wday" "yday" "isdst"
> >
> > $tzone
> > [1] "" "CET" "CEST"
> >
> > $class
> > [1] "POSIXt" "POSIXlt"
> >
> > y[1] <- NA
> > attributes(y)
> > $names
> > [1] "sec" "min" "hour" "mday" "mon" "year" "wday" "yday" "isdst"
> >
> > $tzone
> > [1] "" "CET" "CEST"
> >
> > $class
> > [1] "POSIXt" "POSIXlt"
> >
> > identical(attributes(x), attributes(x1))
> > FALSE
> >
> > identical(attributes(y), attributes(y1))
> > FALSE
> >
> > This can be solved with either:
> >
> > Index: R/src/library/base/R/datetime.R
> > ===================================================================
> > --- R/src/library/base/R/datetime.R (revision 39045)
> > +++ R/src/library/base/R/datetime.R (working copy)
> > @@ -713,10 +713,10 @@
> > {
> > if(!as.logical(length(value))) return(x)
> > value <- as.POSIXlt(value)
> > - cl <- oldClass(x)
> > + att <- attributes(x)
> > class(x) <- class(value) <- NULL
> > for(n in names(x)) x[[n]][i] <- value[[n]]
> > - class(x) <- cl
> > + attributes(x) <- att
> > x
> > }
> >
> > or in the same way as it is done in [.<-POSIXct method
> >
> > Index: R/src/library/base/R/datetime.R
> > ===================================================================
> > --- R/src/library/base/R/datetime.R (revision 39045)
> > +++ R/src/library/base/R/datetime.R (working copy)
> > @@ -714,9 +714,11 @@
> > if(!as.logical(length(value))) return(x)
> > value <- as.POSIXlt(value)
> > cl <- oldClass(x)
> > + tz <- attr(x, "tzone")
> > class(x) <- class(value) <- NULL
> > for(n in names(x)) x[[n]][i] <- value[[n]]
> > class(x) <- cl
> > + attr(x, "tzone") <- tz
> > x
> > }
> >
> > I have checked both versions in r-devel with make check-all and all went
> > fine.
> >
> > Regards, Gregor
> >
> >
> >
>
>
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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