Re: [Rd] sapply improvements

From: Martin Maechler <maechler_at_stat.math.ethz.ch>
Date: Thu, 05 Nov 2009 10:05:16 +0100

>>>>> "PD" == Peter Dalgaard <p.dalgaard_at_biostat.ku.dk> >>>>> on Thu, 05 Nov 2009 00:28:51 +0100 writes:

    PD> William Dunlap wrote: ...
    >>> 
    >>> if (x <= 0) NA else log(x)
    >>> 
    >>> variety otherwise.

>>
>> Would you only want it to coerce upwards to FUN.VALUES's
>> type? E.g., allow sapply(z, length,
>> FUN.VALUE=numeric(1)) to return a numeric vector but die
>> on sapply(z, function(zi)as.complex(zi[1]),
>> FUN.VALUE=numeric(1)) If the latter doesn't die should it
>> return a complex or a numeric vector? (I'd say it needs
>> to be numeric, but I'd prefer that it died.)
    PD> I'd say that it should probably die on downwards
    PD> coercion. Getting a double when an integer is expected,
    PD> or complex instead of double as you indicate, is a
    PD> likely user error. If not, then the user can always
    PD> coerce explicitly inside FUN.

I agree with Peter: Do allow coercion downwards

    PD> Another issue is whether one would want to go beyond the
    PD> base classes of S (logical, integer, double, complex,
    PD> character). For other classes, there may be no notion of
    PD> "up" and "down" in coercion. Then again, sapply was
    PD> always limited to what unlist() will handle, so e.g.

>> sapply(1:10,FUN=function(i)Sys.Date())
    PD> [1] 14553 14553 14553 14553 14553 14553 14553 14553     PD> 14553 14553

    PD> as opposed to

>> structure(rep(14553,10), class="Date")

    PD>   [1] "2009-11-05" "2009-11-05" "2009-11-05"
    PD> "2009-11-05" "2009-11-05" [6] "2009-11-05" "2009-11-05"
    PD> "2009-11-05" "2009-11-05" "2009-11-05"

Well, using    
      as(<prelim_result>,  class(<prototype>) )

would be really nice here....
but alas, we are still not allowed to use as(.,.) in base code which I'd tend to call a "design bug" nowadays..

Martin



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