Stream: helpdesk (published)

Topic: ✔ Finding `extrema` with custom order relation

Júlio Hoffimann (Mar 14 2025 at 18:54):

Suppose I have a vector of objects that implement a partial order < It is not a total order as implemented in isless.

How can I find the extrema of this vector with this custom <? Is there an alternative function that is not hard-coded with isless?

Mason Protter (Mar 14 2025 at 20:11):

I think you can just write

my_extrema(f, itr; kwargs...) = mapreduce(my_extrema_op, itr; kwargs...) do x
    y = f(x)
    (y, y)
end

my_extrema_op((min1, max1), (min2, max2)) = (my_min(min1, min2), my_max(max1, max2))

my_min(x, y) = ifelse(x < y, x, y)
my_max(x, y) = ifelse(x < y, y, x)

Mason Protter (Mar 14 2025 at 20:13):

That's a rough copy of the code here: https://github.com/JuliaLang/julia/blob/master/base/reduce.jl#L844-L854 but using my_min and my_max that should utilize < rather than isless.

Júlio Hoffimann (Mar 14 2025 at 20:29):

Thank you @Mason Protter. I think the issue is still open regarding the customization of isless in Base functions.

Notification Bot (Mar 14 2025 at 20:29):

Júlio Hoffimann has marked this topic as resolved.

Last updated: Apr 25 2025 at 04:43 UTC