Hello,
Inline.
Às 16:44 de 30/08/2018, William Dunlap via R-devel escreveu:
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?
I expect R to continue to do
f0(FALSE, NA) # [1] NA
f0(NA, FALSE) # [1] NA
g0(TRUE, NA) # [1] NA
g0(NA, TRUE) # [1] NA
f1(FALSE, NA)
#Error in if (y) { : missing value where TRUE/FALSE needed
f1(NA, FALSE)
#Error in if (x) { : missing value where TRUE/FALSE needed
g1(TRUE, NA)
#Error in if (x) { : missing value where TRUE/FALSE needed
g1(NA, TRUE)
#Error in if (x) { : missing value where TRUE/FALSE needed
Please don't change this.
There's more to the logical operators than the operands' lengths. That
issue needs to be fixed but it doesn't mean a radical change should happen.
And the same goes for 'if'. Here the problem is completely different,
there's more to 'if' than '||' and '&&'. Any change should be done with
increased care. (Which I'm sure will, as always.)
Rui Barradas
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Thu, Aug 30, 2018 at 7:16 AM, Hadley Wickham <h.wick...@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.bengts...@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
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