[Rd] ROBUSTNESS: x || y and x && y to give warning/error if length(x) != 1 or length(y) != 1

[Emil Bode]

I have to disagree, I think one of the advantages of '||' (or &&) is the lazy evaluation, i.e. you can use the first condition to "not care" about the second (and stop errors from being thrown).
So if I want to check if x is a length-one numeric with value a value between 0 and 1, I can do 'class(x)=='numeric' && length(x)==1 && x>0 && x<1'.
In your proposal, having x=c(1,2) would throw an error or multiple warnings.
Also code that relies on the second argument not being evaluated would break, as we need to evaluate y in order to know length(y)
There may be some benefit in checking for length(x) only, though that could also cause some false positives (e.g. 'x==-1 || length(x)==0' would be a bit ugly, but not necessarily wrong, same for someone too lazy to write x[1] instead of x).

And I don’t really see the advantage. The casting to length one is (I think), a feature, not a bug. If I have/need a length one x, and a length one y, why not use '|' and '&'? I have to admit I only use them in if-statements, and if I need an error to be thrown when x and y are not length one, I can use the shorter versions and then the if throws a warning (or an error for a length-0 or NA result).

I get it that for someone just starting in R, the differences between | and || can be confusing, but I guess that's just the price to pay for having a vectorized language.

Best regards, 
Emil Bode
 
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On 29/08/2018, 05:03, "R-devel on behalf of Henrik Bengtsson" <r-devel-bounces using r-project.org on behalf of 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
    
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