[ruby-core:94901] [Ruby master Feature#16146] Array .difference allow custom comparison

Issue #16146 has been updated by Dan0042 (Daniel DeLorme).


What you're asking for is a O(n operation. I'm not sure it's a good idea to make that so easy and transparent as a core method.

This is quite easy to code and makes the (inefficiency of) two loops more apparent:
```ruby
all.reject{ |a| set.find{ |s| s.val == a.val } }
```

The one advantage I can see to the <=> comparator tough is that it could possibly result in an algorithm more efficient than O(nイ). The implementation could sort the two lists and then do a diff-like operation.
```ruby
only_all,intersection,only_subset = all.uniqdiff3(subset){ |a,b| a.val <=> b.val }
union = only_all + intersection + only_subset
```


----------------------------------------
Feature #16146: Array .difference allow custom comparison
https://bugs.ruby-lang.org/issues/16146#change-81515

* Author: ngomez (Nancy Gomez)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Hello!

I wanted to know if there's any plan to implement the ability to define comparison between individual items in arrays.

Here is where I originally asked the question on Stack Overflow: https://stackoverflow.com/questions/57316775/is-there-any-way-to-specify-how-to-compare-of-array-of-objects-for-difference-f

But specifically, I noticed nearly all the existing Array functions allow us to define ways for comparison, such as #uniq but #difference does not :( This is quite unfortunate but I'm hoping it's just because this function was introduced in 2.6.0, and hopefully this feature can be implemented?

Thanks for any and all info :)



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