Re: [R] Is simplify2array working for dimension > 2?
Re your mention in your other mail (which didn't go to r-help) of this part of the doc: "The default value, TRUE, returns a vector or matrix if appropriate, whereas if simplify = "array" the result may be an array of “rank” (==length(dim(.))) **one higher than the result of FUN(X[[i]]).**" It's not I understood this, but it makes some sense: sapply(1:2, function(i) diag(3)) is a matrix, but sapply(1:2, function(i) diag(3), simplify = "array") is a rank-3 array. So this is the "appropriate case", and recursively simplifying nested list to high rank arrays is not something that's supposed to be done. And indeed, simplify2array(list(diag(2), diag(2))) does yield a rank-3 array as well. And it works for a list of rank-3 arrays, converted to rank-4, etc. So list of array is ok, list of list is not, except for rank 2. The behavior for rank 2 led me to think it applied as well for higher rank, and the doc for the 'higher' argument seemed to confirm this, but I was a bit optimistic. Thanks for your answer. I believe the doc may be improved a little bit, but the intent looks clearer now. Le jeu. 8 févr. 2024 à 10:32, Bert Gunter a écrit : > Jean-Claude: > > Well, here's my "explanation". Caveat emptor! > > Note that: > "simplify2array() is the utility called from sapply() when simplify is > not false" > > and > > > sapply(a, I, simplify = "array") > [,1] [,2] > [1,] list,2 list,2 > [2,] list,2 list,2 > > So it seems that simplify2array() is not intended to operate in the > way that you expected, i.e. that recursive simplification is done. > And, indeed, if you check the code for the function, you will see that > that is the case. Perhaps the key phrase in the docs is in the > sapply() part that says: > > "sapply is a user-friendly version and wrapper of lapply by default > returning a vector, matrix or, if simplify = "array", an array ***if > appropriate***, by applying simplify2array(). " In other words, > recursive simplification is considered not "appropriate". > > FWIW I also find this somewhat confusing and think that explicitly > saying that recursive simplification is not done might make it less > so. But writing docs that address all our possible misconceptions is > pretty difficult (or impossible!), and maybe adding that explicit > caveat would confuse others even more... :-( > > Cheers, > Bert > > > > > > > > > > On Thu, Feb 8, 2024 at 12:12 AM Jean-Claude Arbaut > wrote: > > > > Reading the doc for ?simplify2array, I got the impression that with the > > 'higher = T' argument the function returns an array of dimension greater > > than 2 when it makes sense (the doc says "when appropriate", which is > > rather vague). I would expect > > > > a <- list( > > list(list(1, 2), list(3, 4)), > > list(list(5, 6), list(7, 8)) > > ) > > simplify2array(a, higher = T) > > > > to return the same (possibly up to a dimension permutation) as > > array(1:8, dim = c(2, 2, 2)) > > > > However, in this case simplify2array returns a matrix (i.e. 2 dimensional > > array), whose elements are lists. > > It's the same as > > structure(list(list(1, 2), list(3, 4), list(5, 6), list(7, 8)), dim = > c(2, > > 2)) > > > > I get the same behavior with > > a <- list( > > list(c(1, 2), c(3, 4)), > > list(c(5, 6), c(7, 8)) > > ) > > but then the matrix elements are numeric vectors instead of lists. > > > > Did I miss something to get the result I expected with this function? Or > is > > it a bug? Or maybe the function is not supposed to return a higher > > dimensional array, and I didn't understand the documentation correctly? > > > > There is a workaround, one can do for instance > > array(unlist(a), dim = c(2, 2, 2)) > > and there may be better options (checking dimensions?). > > > > In case it's important: running R 4.3.2 on Debian 12.4. > > > > Best regards, > > > > Jean-Claude Arbaut > > > > [[alternative HTML version deleted]] > > > > __ > > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Is simplify2array working for dimension > 2?
Jean-Claude: Well, here's my "explanation". Caveat emptor! Note that: "simplify2array() is the utility called from sapply() when simplify is not false" and > sapply(a, I, simplify = "array") [,1] [,2] [1,] list,2 list,2 [2,] list,2 list,2 So it seems that simplify2array() is not intended to operate in the way that you expected, i.e. that recursive simplification is done. And, indeed, if you check the code for the function, you will see that that is the case. Perhaps the key phrase in the docs is in the sapply() part that says: "sapply is a user-friendly version and wrapper of lapply by default returning a vector, matrix or, if simplify = "array", an array ***if appropriate***, by applying simplify2array(). " In other words, recursive simplification is considered not "appropriate". FWIW I also find this somewhat confusing and think that explicitly saying that recursive simplification is not done might make it less so. But writing docs that address all our possible misconceptions is pretty difficult (or impossible!), and maybe adding that explicit caveat would confuse others even more... :-( Cheers, Bert On Thu, Feb 8, 2024 at 12:12 AM Jean-Claude Arbaut wrote: > > Reading the doc for ?simplify2array, I got the impression that with the > 'higher = T' argument the function returns an array of dimension greater > than 2 when it makes sense (the doc says "when appropriate", which is > rather vague). I would expect > > a <- list( > list(list(1, 2), list(3, 4)), > list(list(5, 6), list(7, 8)) > ) > simplify2array(a, higher = T) > > to return the same (possibly up to a dimension permutation) as > array(1:8, dim = c(2, 2, 2)) > > However, in this case simplify2array returns a matrix (i.e. 2 dimensional > array), whose elements are lists. > It's the same as > structure(list(list(1, 2), list(3, 4), list(5, 6), list(7, 8)), dim = c(2, > 2)) > > I get the same behavior with > a <- list( > list(c(1, 2), c(3, 4)), > list(c(5, 6), c(7, 8)) > ) > but then the matrix elements are numeric vectors instead of lists. > > Did I miss something to get the result I expected with this function? Or is > it a bug? Or maybe the function is not supposed to return a higher > dimensional array, and I didn't understand the documentation correctly? > > There is a workaround, one can do for instance > array(unlist(a), dim = c(2, 2, 2)) > and there may be better options (checking dimensions?). > > In case it's important: running R 4.3.2 on Debian 12.4. > > Best regards, > > Jean-Claude Arbaut > > [[alternative HTML version deleted]] > > __ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
[R] Is simplify2array working for dimension > 2?
Reading the doc for ?simplify2array, I got the impression that with the 'higher = T' argument the function returns an array of dimension greater than 2 when it makes sense (the doc says "when appropriate", which is rather vague). I would expect a <- list( list(list(1, 2), list(3, 4)), list(list(5, 6), list(7, 8)) ) simplify2array(a, higher = T) to return the same (possibly up to a dimension permutation) as array(1:8, dim = c(2, 2, 2)) However, in this case simplify2array returns a matrix (i.e. 2 dimensional array), whose elements are lists. It's the same as structure(list(list(1, 2), list(3, 4), list(5, 6), list(7, 8)), dim = c(2, 2)) I get the same behavior with a <- list( list(c(1, 2), c(3, 4)), list(c(5, 6), c(7, 8)) ) but then the matrix elements are numeric vectors instead of lists. Did I miss something to get the result I expected with this function? Or is it a bug? Or maybe the function is not supposed to return a higher dimensional array, and I didn't understand the documentation correctly? There is a workaround, one can do for instance array(unlist(a), dim = c(2, 2, 2)) and there may be better options (checking dimensions?). In case it's important: running R 4.3.2 on Debian 12.4. Best regards, Jean-Claude Arbaut [[alternative HTML version deleted]] __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
