[Rd] ROBUSTNESS: x || y and x && y to give warning/error if length(x) != 1 or length(y) != 1
William Dunlap
wdunl@p @ending from tibco@com
Thu Aug 30 17:44:43 CEST 2018
Should the following two functions should always give the same result,
except for possible differences in the 'call' component of the warning
or error message?:
f0 <- function(x, y) x || y
f1 <- function(x, y) if (x) { TRUE } else { if (y) {TRUE } else { FALSE }
}
And the same for the 'and' version?
g0 <- function(x, y) x && y
g1 <- function(x, y) if (x) { if (y) { TRUE } else { FALSE } } else {
FALSE }
The proposal is to make them act the same when length(x) or length(y) is
not 1.
Should they also act the same when x or y is NA? 'if (x)' currently stops
if is.na(x)
and 'x||y' does not. Or should we continue with 'if' restricted to
bi-valued
logical and '||' and '&&' handling tri-valued logic?
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Thu, Aug 30, 2018 at 7:16 AM, Hadley Wickham <h.wickham using gmail.com> wrote:
> I think this is an excellent idea as it eliminates a situation which
> is almost certainly user error. Making it an error would break a small
> amount of existing code (even if for the better), so perhaps it should
> start as a warning, but be optionally upgraded to an error. It would
> be nice to have a fixed date (R version) in the future when the
> default will change to error.
>
> In an ideal world, I think the following four cases should all return
> the same error:
>
> if (logical()) 1
> #> Error in if (logical()) 1: argument is of length zero
> if (c(TRUE, TRUE)) 1
> #> Warning in if (c(TRUE, TRUE)) 1: the condition has length > 1 and only
> the
> #> first element will be used
> #> [1] 1
>
> logical() || TRUE
> #> [1] TRUE
> c(TRUE, TRUE) || TRUE
> #> [1] TRUE
>
> i.e. I think that `if`, `&&`, and `||` should all check that their
> input is a logical (or numeric) vector of length 1.
>
> Hadley
>
> On Tue, Aug 28, 2018 at 10:03 PM Henrik Bengtsson
> <henrik.bengtsson using gmail.com> wrote:
> >
> > # Issue
> >
> > 'x || y' performs 'x[1] || y' for length(x) > 1. For instance (here
> > using R 3.5.1),
> >
> > > c(TRUE, TRUE) || FALSE
> > [1] TRUE
> > > c(TRUE, FALSE) || FALSE
> > [1] TRUE
> > > c(TRUE, NA) || FALSE
> > [1] TRUE
> > > c(FALSE, TRUE) || FALSE
> > [1] FALSE
> >
> > This property is symmetric in LHS and RHS (i.e. 'y || x' behaves the
> > same) and it also applies to 'x && y'.
> >
> > Note also how the above truncation of 'x' is completely silent -
> > there's neither an error nor a warning being produced.
> >
> >
> > # Discussion/Suggestion
> >
> > Using 'x || y' and 'x && y' with a non-scalar 'x' or 'y' is likely a
> > mistake. Either the code is written assuming 'x' and 'y' are scalars,
> > or there is a coding error and vectorized versions 'x | y' and 'x & y'
> > were intended. Should 'x || y' always be considered an mistake if
> > 'length(x) != 1' or 'length(y) != 1'? If so, should it be a warning
> > or an error? For instance,
> > '''r
> > > x <- c(TRUE, TRUE)
> > > y <- FALSE
> > > x || y
> >
> > Error in x || y : applying scalar operator || to non-scalar elements
> > Execution halted
> >
> > What about the case where 'length(x) == 0' or 'length(y) == 0'? Today
> > 'x || y' returns 'NA' in such cases, e.g.
> >
> > > logical(0) || c(FALSE, NA)
> > [1] NA
> > > logical(0) || logical(0)
> > [1] NA
> > > logical(0) && logical(0)
> > [1] NA
> >
> > I don't know the background for this behavior, but I'm sure there is
> > an argument behind that one. Maybe it's simply that '||' and '&&'
> > should always return a scalar logical and neither TRUE nor FALSE can
> > be returned.
> >
> > /Henrik
> >
> > PS. This is in the same vein as
> > https://mailman.stat.ethz.ch/pipermail/r-devel/2017-March/073817.html
> > - in R (>=3.4.0) we now get that if (1:2 == 1) ... is an error if
> > _R_CHECK_LENGTH_1_CONDITION_=true
> >
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>
>
> --
> http://hadley.nz
>
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