On Thu, 3 Dec 2020 19:06:18 -0500 Allen Madsen <allen.c.mad...@gmail.com> wrote:
> Enum.compare_count([], 1) #=> :lt > Enum.compare_count([1], 1) #=> :eq > Enum.compare_count([1, 2], 1) #=> :gt This is the way to go, because in one function call we can determine the course of the action, such as in case Enum.compare_count(list, n) do :lt -> ... :eq -> ... :gt -> ... end when using the predicate functions it would require at least two function calls. > > Allen Madsen > http://www.allenmadsen.com > > > On Thu, Dec 3, 2020 at 6:51 PM Zach Daniel > <zachary.s.dan...@gmail.com> wrote: > > > Well, List.count doesn’t exist yet, but either way it sounds like > > not a great idea :) I couldn’t find examples in other Lang’s, so > > maybe I’ll just throw out some other names: > > > > Enum.at_least?/2 > > > > Enum.at_most?/2 > > > > Enum.has_count?/2 > > > > On Thu, Dec 3, 2020 at 5:14 PM Michał Muskała <mic...@muskala.eu> > > wrote: > > > >> Unfortunately this can’t be done automatically since it has subtle > >> semantic differences. In particular Enum.count/1 (or length/1) not > >> only traverses the list to count its size, but also verifies it’s > >> a proper list raising an exception for improper lists. The > >> difference could be seen for value like: > >> > >> > >> > >> [1, 2, 3 | :invalid] > >> > >> > >> > >> Calling length/1 or Enum.count/1 on this raises. If compiler did > >> the optimisation you propose, for something like length(list) > 0, > >> it wouldn’t fully traverse the list and wouldn’t raise. Thus such > >> an optimisation is not possible in the general case. > >> > >> > >> > >> *From: *elixir-lang-core@googlegroups.com < > >> elixir-lang-core@googlegroups.com> > >> *Date: *Thursday, 3 December 2020 at 22:04 > >> *To: *elixir-lang-core@googlegroups.com < > >> elixir-lang-core@googlegroups.com> > >> *Subject: *Re: [elixir-core:9802] Proposal `Enum.more_than?/2` or > >> `List.more_than?/2` > >> > >> This probably off the table/unreasonable, but it also seems like > >> something that could be statically solved and people would never > >> need to know as it is just an optimization. E.g Enum.count(list) > > >> n could optimized by the compiler? Probably wouldn’t be good for > >> all Enums, since counting would be expected to enumerate them, so > >> maybe only something like List.count 🤷♂️ > >> > >> > >> > >> On Thu, Dec 3, 2020 at 1:42 PM Zach Daniel > >> <zachary.s.dan...@gmail.com> wrote: > >> > >> Another benefit to the options list would be supporting it for > >> count with a predicate, e.g Enum.count(enum, &some_predicate/1, > >> max: 4) > >> > >> > >> > >> On Thu, Dec 3, 2020 at 1:35 PM Zach Daniel > >> <zachary.s.dan...@gmail.com> wrote: > >> > >> Nothing is jumping out at me from elsewhere yet, but another > >> option might be accepting options in `Enum.count`, like > >> `Enum.count(list, max: 4)`. I’ll keep searching though. > >> > >> > >> > >> On Thu, Dec 3, 2020 at 1:31 PM Zach Daniel > >> <zachary.s.dan...@gmail.com> wrote: > >> > >> I agree on the name feeling subpar :) I’ll take a look and see if > >> I can find other examples. > >> > >> > >> > >> On Thu, Dec 3, 2020 at 12:21 PM José Valim <jose.va...@dashbit.co> > >> wrote: > >> > >> Thanks Zach! I like this idea but the proposed name, for some > >> reason, doesn't sit right with me. Is there any prior art from > >> other langs we could look at? > >> > >> > >> > >> On Thu, Dec 3, 2020 at 6:15 PM Zachary Daniel > >> <zachary.s.dan...@gmail.com> wrote: > >> > >> Counting a list, especially a large one, to know if there are > >> "more than x" or "less than x" items is inefficient. > >> > >> > >> > >> Right now I often see things like `if Enum.count(list) > 4 ...`, > >> mostly because writing a recursive `more_than?` check is tedious, > >> or doing something like `Enum.empty?(Enum.drop(list, 4))` is not > >> very expressive. > >> > >> > >> > >> I think it would be nice to have an `Enum.more_than?` that does > >> that work for you. It could also be `List.more_than?/2` if we > >> don't want it in Enum. 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