[ruby-core:87673] [Ruby trunk Feature#11076] Enumerable method count_by

Issue #11076 has been updated by baweaver (Brandon Weaver).


Has there been any thought on this as a language feature?

There was an earlier conversation demonstrating a practical use for this feature, and I had mentioned a few of the core maintainers to bring the subject back into consideration:

https://twitter.com/keystonelemur/status/1012434696909852672

nobu had recently updated his patch here:

https://github.com/ruby/ruby/compare/trunk...nobu:feature/11076-Enumerable%23count_by

I still believe this would be an incredibly useful feature to have in the core of the language, as a very common pattern to work around it is unintuitive for newer programmers:

```
# Most common
array
  .group_by { |v| v }
  .map { |k, v| [k, v.size] }
  .to_h

# In older versions:
Hash[array.group_by { |v| v }.map { |k, v| [k, v.size] }]

# or in more recent versions:
array
  .group_by { |v| v }
  .transform_values(&:size)

# or using reduce / ewo:
array.each_with_object(Hash.new(0)) { |v, h| h[v] += 1 }
```

By giving a name to this concept, we've made it more accessible as well. Given the current trend of 2.6, I believe this would be a welcome addition.

----------------------------------------
Feature #11076: Enumerable method count_by
https://bugs.ruby-lang.org/issues/11076#change-72696

* Author: haraldb (Harald B旦ttiger)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
I very often use `Hash[array.group_by{|x|x}.map{|x,y|[x,y.size]}]`.

Would be nice with to have a method called `count_by`:

~~~ruby
array = ['aa', 'aA', 'bb', 'cc']
p array.count_by(&:downcase) #=> {'aa'=>2,'bb'=>1,'cc'=>1}
~~~



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