Hi Joseph This behaviour is as expected (and as documented by ?`[`) because the default of drop=TRUE coerces the result to the lowest possible dimension, which in your case is a vector rather than array. Using for example:
b[1,,,drop=FALSE] ... results in an output array with the same number of dimensions (i.e. length of dim()) as the input array. I always use drop=FALSE when programming in situations where the dimensions of the input array aren't known (and forgetting to do so has several times bitten me when I later come to pass in an array like yours). I am not aware of a way to make the extract operator behave as you apparently expected (drop the dimension corresponding to the supplied length-1 index but leaving all others even if they are also length 1). If you want this behaviour then you would be best to create a wrapper function, or perhaps even a derived class, but that is not a topic for r-devel (rather r-help). Best wishes, Matt On 30/09/2023, 05:28, "R-devel on behalf of Joseph Wood" <r-devel-boun...@r-project.org <mailto:r-devel-boun...@r-project.org> on behalf of jwood...@gmail.com <mailto:jwood...@gmail.com>> wrote: [You don't often get email from jwood...@gmail.com <mailto:jwood...@gmail.com>. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification <https://aka.ms/LearnAboutSenderIdentification> ] Hello, I recently discovered a possible inconsistency with usage of an object of class array. Consider the following example: ## Setup a <- array(1:6, dim = c(1, 3, 2)) a , , 1 [,1] [,2] [,3] [1,] 1 2 3 , , 2 [,1] [,2] [,3] [1,] 4 5 6 class(a) [1] "array" dim(a) [1] 1 3 2 ## Now use `[` a[1,,] [,1] [,2] [1,] 1 4 [2,] 2 5 [3,] 3 6 class(a[1,,]) [1] "matrix" "array" dim(a[1,,]) [1] 3 2 Up until this point, it makes sense to me. Now, let's consider when dim = c(1, 6, 1). This is where I have a little trouble understanding the behavior. ## Array with dim = c(1, any_number_here, 1) b <- array(1:6, dim = c(1, 6, 1)) b , , 1 [,1] [,2] [,3] [,4] [,5] [,6] [1,] 1 2 3 4 5 6 class(b) [1] "array" dim(b) [1] 1 6 1 ## The problem b[1,,] [1] 1 2 3 4 5 6 dim(b[1,,]) NULL class(b[1,,]) [1] "integer" I would have expected: b[1,,] ## produced the output with matrix(1:6, ncol = 1) [,1] [1,] 1 [2,] 2 [3,] 3 [4,] 4 [5,] 5 [6,] 6 class(b[1,,]) [1] "matrix" "array" dim(b[1,,]) [1] 3 1 Is this a bug? If not, any help understanding this behaviour would be much appreciated. Thanks, Joseph [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org <mailto:R-devel@r-project.org> mailing list https://stat.ethz.ch/mailman/listinfo/r-devel <https://stat.ethz.ch/mailman/listinfo/r-devel> ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
