The lt keyword for issorted and sort! is defying my intuition. From reading the source code, I understand why I get the following results, but I am finding it counterintuitive. From the documentation for sort!: the lt keyword allows providing a custom “less than” function Let’s try it: julia> …

[image] Oscar_Smith: The reason for this design is it only relies on users to define ==(a::T,b::T) and <(a::T,b::T) . That is not correct. All you need is < / isless. Take for example julia> mutable struct Wrap _::Int end julia> Base.isless(a::Wrap, b::Wrap) = isless(a._, b._…

[image] Jean_Michel: and that is much more than 1% of users. The number was for the sake of argument. But how big do you think that number is? And as I said, the docs don’t even mention “total order” (or do they), so why would I expect that to be relevant?

[image] DNF: And as I said, the docs don’t even mention “total order” (or do they), so why would I expect that to be relevant? The documentation for Base.isless does mention “total order” ( Understanding issorted's lt keyword - #2 by goretkin ) . And isless is the default argument. The connecti…

The default argument creates(?) a total ordering, but it doesn’t follow that all arguments must do so. Oh, well, it’s getting late. Maybe sleeping on it will help.

[image] goretkin: It sounds like you are willing to accept the claim that isless and isequal is more fundamental than <= . I don’t see a ranking of fundamentalness between < and <=. It’s possible to define either in terms of the other. A total order is normally defined in terms of <=. Checki…

[image] sostock: [image] mkitti: Are sort ∘ unique and allunique(seq) && issorted(seq) really the most efficient way to accomplish those tasks? No, the most efficient would probably be a loop. My contention is that issorted already contains that loop. What I’m not sure about is if I wo…

[image] jzr: I don’t see a ranking of fundamentalness between < and <=. It’s possible to define either in terms of the other. Yes, both choices are possible. And a choice has already been made. This allows Base to have fallback methods. Can you explain what you don’t see here in the previous…

[image] goretkin: That it is defined in terms of something like isless is reasonable. I don’t think running isstrictlysorted(::ArrayWithDuplicates) is usually the user’s intent when they run issorted(lst), and having footguns lying around is a bad property in a language. [image] goretkin: …

[image] jzr: I don’t think running isstrictlysorted(::ArrayWithDuplicates) is reasonable First of all, what does this mean? Secondly, just because the answer to something is false, doesn’t mean it’s unreasonable to ask the question. Please show an actual piece of code that you think is a foo…

Yeah I deleted that line :slight_smile:

Understanding issorted's lt keyword

New to Julia

mkitti May 12, 2021, 8:47pm 73

My contention is that issorted already contains that loop. What I’m not sure about is if I would be I’m exploiting documented behavior or an implementation detail by using issorted( ..., lt = <=).

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Understanding issorted's lt keyword

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