On 19/08/2019 10:19 a.m., Kirill Müller wrote:
Hi everyone
The following behavior (in R 3.6.1 and R-devel r77040) caught me by
surprise today:
truthy <- c(TRUE, FALSE)
falsy <- c(FALSE, TRUE, FALSE)
if (truthy) "check"
#> Warning in if (truthy) "check": the condition has length > 1 and only the
#> first element will be used
#> [1] "check"
if (falsy) "check"
#> Warning in if (falsy) "check": the condition has length > 1 and only the
#> first element will be used
if (FALSE || truthy) "check"
#> [1] "check"
if (FALSE || falsy) "check"
if (truthy || FALSE) "check"
#> [1] "check"
if (falsy || FALSE) "check"
The || operator gobbles the warning about a length > 1 vector. I wonder
if the existing checks for length 1 can be extended to the operands of
the || and && operators. Thanks (and apologies if this has been raised
before).
This seems to be an August topic. It was discussed last year in a long
thread starting with this message:
https://stat.ethz.ch/pipermail/r-devel/2018-August/076678.html
I think there was general agreement that it would be a good idea to add
some warnings. News for R 3.6.0 includes this:
"Experimentally, setting environment variable _R_CHECK_LENGTH_1_LOGIC2_
will lead to warnings (or errors if the variable is set to a ‘true’
value) when && or || encounter and use arguments of length more than one."
You get a warning if you set that variable to "warn", you get an error
if you set it to "true".
Duncan Murdoch
Duncan Murdoch
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