Feature #6847: Hash#extract

• Status: Rejected
• Assignee: matz (Yukihiro Matsumoto)
• Target version: 2.6

[citizen428 (Michael Kohl)]

I often need a method to extract "subhashes" from hashes. I often monkey-patched this into hash and found "extract" to be a good name for the method. Afterwards I found out that there actually is a mutating method called "extract!" in ActiveSupport, so I guess the name is kinda established. Here's the Ruby version from my private extension library, if there's any interest in this I would try to re-implement it in C:

class Hash
def extract(*ks)
existing = keys & ks
Hash[existing.zip(values_at(*existing))]
end
end

[claytrump (Clay Trump)]

Isn't that like the method slice in ActiveSupport?

On Thu, Aug 9, 2012 at 1:01 PM, citizen428 (Michael Kohl) <
[e-mail]> wrote:

Issue #6847 has been reported by citizen428 (Michael Kohl).

---

Feature #6847: Hash#extract
https://bugs.ruby-lang.org/issues/6847

Author: citizen428 (Michael Kohl)
Status: Open
Priority: Normal
Assignee:
Category: core
Target version:

I often need a method to extract "subhashes" from hashes. I often
monkey-patched this into hash and found "extract" to be a good name for the
method. Afterwards I found out that there actually is a mutating method
called "extract!" in ActiveSupport, so I guess the name is kinda
established. Here's the Ruby version from my private extension library, if
there's any interest in this I would try to re-implement it in C:

class Hash
def extract(*ks)
existing = keys & ks
Hash[existing.zip(values_at(*existing))]
end
end

--
http://bugs.ruby-lang.org/

--

[citizen428 (Michael Kohl)]

claytrump (Clay Trump) wrote:

Isn't that like the method slice in ActiveSupport?

It's definitely like extract! in ActiveSupport, just non-destructive. I still think this is useful enough to be in core though. I needed it repeatedly, I know other people who regularly monkey-patch it into Hash and not everyone wants to drag ActiveSupport into their non-Rails projects. I don't insist on it of course, but it wouldn't be the first thing to make it from an extensions library into core, think of Symbol#to_proc for example.

[trans (Thomas Sawyer)]

Ruby Facets has Hash#slice as well.

http://rdoc.info:8080/github/rubyworks/facets/master/Hash#slice-instance_method

+1 for its addition of Hash.

[claytrump (Clay Trump)]

It's definitely like extract! in ActiveSupport, just non-destructive.

There is no "extract!" in ActiveSupport, its "slice!" you mean.

So yeah, I've used that before, and would be nice in core. I think it
should be called 'slice' instead of 'extract'. It's a better name and it
already exists like that in ActiveSupport and in Facets...

--

[citizen428 (Michael Kohl)]

claytrump (Clay Trump) wrote:

There is no "extract!" in ActiveSupport, its "slice!" you mean.

http://apidock.com/rails/Hash/extract%21

File activesupport/lib/active_support/core_ext/hash/slice.rb, line 35

def extract!(*keys)
result = {}
keys.each {|key| result[key] = delete(key) }
result
end

[trans (Thomas Sawyer)]

It important to understand the differences and to determine the best definition. ActiveSupport's #slice returns the same type of class, which I think is important, where as #extract! always returns a Hash. Also, #slice and #slice! are provided, where as there is only #extract! in ActiveSupport. Certainly we want both. ActiveSupport's #slice also has a special feature for #convert_key, which I think that would be nice for Ruby to have too, but it is not part of Ruby at this time. So that would obviously be omitted.

I concur with Clay that #slice is the better name b/c Array#[] and Array#slice are pretty much the same, and though it might be a little bit more different that general relationship should also hold for Hash.

[claytrump (Clay Trump)]

Oh my, what a disaster. I wonder who made the crazy decision that hash
slice would returned a slice of the hash and slice! would return... the
receiver and not the slice of the hash. Especially since Array slice and
slice! return the same values...

So, sorry Michael, I was confused. Anyways, I think the most important is
slice and that's the correct name too, and it might be nice to have a
mutating version too. I'd name it slice! and too bad for ActiveRecord, but
that might not be the best way to go.

--

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to matz (Yukihiro Matsumoto)
• Target version set to 2.6

[matz (Yukihiro Matsumoto)]

• Status changed from Assigned to Rejected

Use Hash#select which now returns an hash.

Matz.