From: joshua.goodall@...
Date: 2019-07-16T07:13:33+00:00
Subject: [ruby-core:93811] [Ruby master Feature#15975] Add Array#pluck

Issue #15975 has been updated by inopinatus (Joshua GOODALL).


I think that's pretty limited. #pluck is a fairly crude method, fine for Rails but hardly befitting the Ruby standard library. I'd much rather use a higher-order function and get somewhere much more interesting.

By instead implementing `Array#to_proc` (which doesn't currently exist) as something that applies to_proc to its own elements in turn, we can get somewhere much more interesting:

```ruby
class Array
  def to_proc
    Proc.new do |head, *tail|
      collect(&:to_proc).collect do |ep|
        ep_head = ep[head]
        tail.empty? ? ep_head : [ep_head] + tail.collect(&ep)
      end
    end
  end
end
```

we can now do some very nice things just with existing syntax:

```ruby
# data
people = [{name: "Park", age: 42}, {name: "Lee", age: 31}]
keys = people.keys

# single item extraction
:name.then &people      #=> ["Park", "Lee"]
people.to_proc[:name]   #=> ["Park", "Lee"]

# multiple item extraction
keys.then &people            #=> [["Park", 42], ["Lee", 31]]
people.to_proc[:name, :age]  #=> [["Park", 42], ["Lee", 31]]

# multiple invocation
names.map(&[:upcase, :length]) #=> [["PARK", 4], ["LEE", 3]]
```

Could work as `Enumerable#to_proc` instead.


----------------------------------------
Feature #15975: Add Array#pluck
https://bugs.ruby-lang.org/issues/15975#change-79679

* Author: lewispb (Lewis Buckley)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Inspired by https://github.com/rails/rails/issues/20339

While developing web applications I've often wanted to quickly extract an array of values from an array of hashes.

With an array of objects, this is possible:

```rb
irb(main):001:0> require 'ostruct'
=> true
irb(main):002:0> [OpenStruct.new(name: "Lewis")].map(&:name)
=> ["Lewis"]
```

This PR adds Array#pluck allowing this:

```rb
irb(main):001:0> [ {name: "Lewis"} ].pluck(:name)
=> ["Lewis"]
```

without this PR:

```rb
irb(main):001:0> [ {name: "Lewis"} ].map { |item| item[:name] }
=> ["Lewis"]
```

Implemented here:

https://github.com/ruby/ruby/pull/2263



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