R devel - Jun 2006 - Ops.Date: promote characters to Dates?

Ops.Date  <- function (e1, e2)
{
    if (nargs() == 1)
        stop("unary ", .Generic, " not defined for Date
objects")
    boolean <- switch(.Generic, "<" = , ">" = ,
"==" = , "!=" = ,
        "<=" = , ">=" = TRUE, FALSE)
    if (!boolean)
        stop(.Generic, " not defined for Date objects")
+    if (!nchar(e1)) e1 <- as.Date(e1)
+    if (!nchar(e2)) e2 <- as.Date(e2)
    NextMethod(.Generic)
}

  adding the above two lines to Ops.Date makes, e.g.

as.Date("1999-12-13") == "1999-06-14"

behave as "expected".

  Does it seem like a good idea?
  (I was inspired by a student's confusion, and by
the fact that Ops.factor does a similar thing -- although
in this case it seems more sensible to promote the
character to a Date rather than demoting the Date
to a character (in which case comparisons might not
work right?))

  Similar questions might apply to Ops.POSIXt ...

  Ben Bolker

Note that the first argument still cannot be character
since Ops.Date won't get dispatched in that case.

On 6/24/06, Ben Bolker <bolker at ufl.edu> wrote:
>  Ops.Date  <- function (e1, e2)
> {
>    if (nargs() == 1)
>        stop("unary ", .Generic, " not defined for Date
objects")
>    boolean <- switch(.Generic, "<" = , ">" = ,
"==" = , "!=" = ,
>        "<=" = , ">=" = TRUE, FALSE)
>    if (!boolean)
>        stop(.Generic, " not defined for Date objects")
> +    if (!nchar(e1)) e1 <- as.Date(e1)
> +    if (!nchar(e2)) e2 <- as.Date(e2)
>    NextMethod(.Generic)
> }
>
>  adding the above two lines to Ops.Date makes, e.g.
>
> as.Date("1999-12-13") == "1999-06-14"
>
> behave as "expected".
>
>  Does it seem like a good idea?
>  (I was inspired by a student's confusion, and by
> the fact that Ops.factor does a similar thing -- although
> in this case it seems more sensible to promote the
> character to a Date rather than demoting the Date
> to a character (in which case comparisons might not
> work right?))
>
>  Similar questions might apply to Ops.POSIXt ...
>
>  Ben Bolker
>
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