If we introduced Covectors and a row slice of a Matrix was a Covector, then this wouldn't be an issue anymore since we could simply allow sorting both Vectors and Covectors but not Matrices. There's still the open question of what taking a slice that looks like T[1,:,1] should produce. That's a one-dimensional slice, but is it a Vector or a Covector?
On Mon, Jul 21, 2014 at 8:53 AM, Leah Hanson <[email protected]> wrote: > I hadn't seen that issue; thanks for the link. I'm glad there's a > discussion going on about that. :) > > -- Leah > > > On Mon, Jul 21, 2014 at 10:43 AM, Ivar Nesje <[email protected]> wrote: > >> Warning for 2d row vectors used in context where only a 1d column vector >> is used could definelty be implemented as help when you get a MethodError. >> >> See also https://github.com/JuliaLang/julia/issues/7512. >> >> Ivar >> >> kl. 16:03:46 UTC+2 mandag 21. juli 2014 skrev Leah Hanson følgende: >>> >>> I agree that the `["a" "b" "c"]` vs `["a", "b", "c"]` syntax is >>> something likely to catch new-to-Julia users. I have personally watched >>> people struggle with that. Programmers familiar with other languages take a >>> bit to understand the vectors vs row-matrixes thing, when they were just >>> expecting a list/array type. While you can read `Array{ASCIIString, 2}` in >>> the REPL response to `["a" "b" "c"]` (and in the `sort` error message), you >>> have to know that matrixes/row-matrixes exist in Julia and that we've >>> chosen not to interpret a row-matrix as a list. >>> >>> I'm not in favor of make `sort` work for row-matrixes. This distinction >>> is an important one to learn as a Julia programmer and you will continue to >>> encounter it. However, maybe our error messages could be a lot better. The >>> most magical version would be to say something like: >>> >>> ~~~ >>> julia> sort(lst) >>> >>> sort(lst) >>> ~~~ >>> `lst` is an Array{ASCIIString, 2}, which `sort` has no method for. >>> Did you mean to define `lst` as `lst = ["a", "b", "c"]`? >>> ~~~ >>> >>> This is most appropriate in a "I just used a row-matrix literal." >>> context, but for any (short) row-matrix, it could be helpful. I use C++ at >>> work, and this is what many of my error messages look like: the line (with >>> line number/file), with the problem underlined/highlighted, a brief >>> description of the problem, and (often) a suggestion of what I may have >>> meant. The suggests are literally copy-paste-able code, not a prose >>> description. >>> >>> I find these to be very useful, especially as a less experienced C++ >>> user. The suggestions appear for things like "->" vs "." (when you've got >>> the wrong one), when you've mistyped a variable name (there's a variable of >>> the proper type in-scope, and you used a non-existant/other-type variable), >>> when you forgot to namespace a variable/function (you used `vector` but >>> have to use `std::vector`). >>> >>> These error messages do a great job of "I'm not going to except your >>> incorrect input, but I do have a solid guess about what you meant, so I'll >>> tell you the answer.". They are probably my favorite thing about using C++, >>> and I think they are the most friendly thing you can do for new users. >>> >>> -- Leah >>> >>> >>> >>> On Mon, Jul 21, 2014 at 6:01 AM, Ivar Nesje <[email protected]> wrote: >>> >>>> 1. It clearly isn't. >>>> >>>> 2. It will not cause any overhead in the common case (because it would >>>> be a separate method in Julia). The question is whether this is a case >>>> where we should guess what the user intended, or force the user to fix a >>>> potential problem. >>>> >>>> Not sure what we could do about this though, because the distinction is >>>> useful and it becomes much more annoying if you discover such subtle >>>> differences later rather than earlier. >>>> >>>> Ivar >>>> >>>> kl. 04:19:53 UTC+2 mandag 21. juli 2014 skrev Abe Schneider følgende: >>>> >>>>> It wasn't obvious to me initially why `sort` wasn't working for me >>>>> (strings and composite types). On further investigation it looks like that >>>>> it only works for single-dimension arrays -- which makes sense. However, >>>>> if >>>>> I type: >>>>> >>>>> lst = ["a" "b" "c"] >>>>> sort(lst) >>>>> >>>>> I get an error. The answer is that it's of type `Array{ASCIIString, >>>>> 2}`, whereas `sort` wants the type to be `Array{ASCIIString, 1}`. The >>>>> correct solution is to write this instead: >>>>> >>>>> lst = ["a", "b", "c"] >>>>> sort(lst) >>>>> >>>>> The problem seems to derive from two design decisions: >>>>> >>>>> 1. It is not obvious to someone new to Julia why one form gives a >>>>> two dimensional array whereas the other gives a one dimensional array. >>>>> 2. `sort` doesn't try to determine if the array passed is actually >>>>> jeust one dimensional. >>>>> >>>>> I'm not sure there is a simple solution. I assume there's a good >>>>> reason for (1) and (2) involves some overhead which might be undesirable. >>>>> >>>> >>> >
