[ruby-core:97311] [Ruby master Feature#16665] Add an Array#except_index method

Issue #16665 has been updated by shevegen (Robert A. Heiler).


I can not comment on how useful this may be; I think I may have added something similar
once in a while, but I can not say how useful or common that would be. IMO we should 
see to determine how common the above idiom is, before we can say that it should be
part of core ruby. (This is not necessarily a con-opinion from me, just that I think
it may be better to assess how useful the addition would be, objectively).

There is one minor complaint that I have and I think it is about the name. The
word "index" is used a lot so I guess we can expect a method that has "index" to
do something with ... an index, or indici/indices - no problem there. But "except"
is quite rare in ruby. Python has try/except clause. I believe that "except" as
word is not completely fitting into ruby's parlance, as-is. I could be wrong :)
but it does not "feel" very ruby-ish.

I can not offer a better alternative, but if we look at other ruby-method names,
we have select, reject, filter ... and .each_with_index, and similar method 
names. It may be best to be slowly considering whether "except" may be a good
addition - not necessarily saying that it may be bad, but I am not sure it is
a great name. (The name can be changed if the underlying suggestion has merit,
so perhaps we should first evaluate whether the functionality is useful, 
before finding an alternative name, or sticking to the suggested name.)

----------------------------------------
Feature #16665: Add an Array#except_index method
https://bugs.ruby-lang.org/issues/16665#change-84436

* Author: alex_golubenko (Alex Golubenko)
* Status: Open
* Priority: Normal
----------------------------------------
The main idea is to implement a method that we can use to exclude elements from the array by their indices.

For example:

``` ruby
%w( a b c d e f).except_index(0, -1) 
=> ["b", "c", "d", "e"]

%w( a b c d e f g h ).except_index(0..1, 3, -2..-1)
=> ["c", "e", "f"]
```

I was meeting many questions on the StackOverflow about how to do such functionality also found many topics about it.
So I think it might a helpful addition.

I spent a few days finding the proper solution on Ruby that might be acceptable with integers and ranges(both positive and negative) and has good performance: 

```ruby
  def except_index(*indexes)
    indexes.each_with_object(dup) do |ind, obj|
      ind.is_a?(Range) ? ind.each { |i| obj[i] = false } : obj[ind] = false
    end.select(&:itself)
  end
```

As you can see it's have not the best readability so I think it's a good point to add a built-in method on C.



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