Dear all,
I just stumbled upon some behavior of the == operator which is at least
somewhat inconsistent.
R version 3.6.1 (2019-07-05) -- "Action of the Toes"
Copyright (C) 2019 The R Foundation for Statistical Computing
Platform: x86_64-w64-mingw32/x64 (64-bit)
> list(a=1:3, b=LETTERS[1:3]) == NULL
logical(0)
> matrix(1:6, 2,3) == NULL
logical(0)
> data.frame(a=1:3, b=LETTERS[1:3]) == NULL # same for == logical(0)
Error in matrix(if (is.null(value)) logical() else value, nrow = nr,
dimnames = list(rn, :
length of 'dimnames' [2] not equal to array extent
> data.frame(NULL) == 1
<0 x 0 matrix>
> data.frame(NULL) == NULL
<0 x 0 matrix>
> data.frame(NULL) == logical(0)
<0 x 0 matrix>
I wonder if data.frame(<some non-empty data>) == NULL should also return
a value instead of an error. R help reads:
"At least one of |x| and |y| must be an atomic vector, but if the other
is a list *R* attempts to coerce it to the type of the atomic vector:
this will succeed if the list is made up of elements of length one that
can be coerced to the correct type.
If the two arguments are atomic vectors of different types, one is
coerced to the type of the other, the (decreasing) order of precedence
being character, complex, numeric, integer, logical and raw."
It is not clear from the help what to expect for NULL or empty atomic
vectors. It is also strange that for list() there is no error but for
data.frame() with the same data an error is thrown. I can see that there
might be reasons to return logical(0) instead of FALSE, but I do not
fully understand why there should be differences between e.g. matrix()
and data.frame().
Also, It is at least somewhat strange that data.frame(NULL) == NULL and
similar expressions return an empty matrix, while comparing a normal
filled matrix to NULL returns logical(0).
Even if this behavior is expected, the error message shown by
data.frame(...) == NULL is not very informative.
Thanks and best regards,
Hilmar
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