Re: pint: Elizabeth, sort list???

> On 3 Mar 2024, at 03:32, ToddAndMargo via perl6-users <[email protected]> wrote:
> 
>> On 3/2/24 05:13, Elizabeth Mattijsen wrote:
>>> <afoo12 afoo2>.sort(*.split(/\d+/, :kv).map({ (try .Numeric) // $_}).List)
> 
>> Hi Elizabeth,
>> It works perfectly.  Thank you!
>> I have no idea why, I will ask you in another post
> Would you take apart your sort piece by piece and explain
> each part?

Actually, the expression can be refined a bit:

say <afoo12 afoo2>.sort(*.split(/\d+/, :v).map({ (try .Int) // $_}).List)

Sort works by using `cmp` semantics by default.

If `cmp` is called on two lists, it will `cmp` each element and return the result of the first comparison that did not produce `Same`.

If you call `sort` with a Callable that takes only one argument, it is taken as the producer of the actual values that will be compared, basically doing a Schwartzian transform under the hood.

A whatever code (which is what we specified here) produces a Callable with a single argument.  So we'll be doing a Schwartzian transform under the hood.

The `split` splits the value (each element in the list) on any set of Numeric characters (`\d+`), *but* also produces the strings that were split on (`:v`). (The previous version had .kv, but that just produces more identical entries in the list, which only will make comparisons slower).

The resulting values from the `split` are then mapped to an integer value (if possible: `(try .Int)` and if that fails, just returns the value (`// $_`).  (The previous version had `.Numeric`, which will also work, but since `\d+` can only produce integers, it's an extra unnecessary step).

Then convert the `.Seq` that is produced by the `.map` to a `List`.  Otherwise we'd be comparing `Seq` objects, and the semantics of those are undefined.

So for `"afoo12" cmp "afoo2"`, we will be doing `("afoo", 12) cmp ("afoo", 2)`.  Which would do: `"afoo" cmp "afoo"`, which produces `Same`, and then do `12 cmp 2`, which will return `More`, and thus will cause swapping the order of <afoo12 afoo2>.


Hope that made sense!