From: "marcandre (Marc-Andre Lafortune)" <ruby-core@...>
Date: 2012-11-14T01:12:57+09:00
Subject: [ruby-core:49310] [ruby-trunk - Feature #7341] Enumerable#associate


Issue #7341 has been updated by marcandre (Marc-Andre Lafortune).

Category changed from lib to core
Priority changed from Low to Normal

Hi,

bitsweat (Jeremy Kemper) wrote:
> In short: associating a collection of keys with calculated values should be easy to do and the code should reflect the programmer's intent.

A strong +1 from me

> See  https://gist.github.com/4035286

A good start. I'd make one important change: return an enumerator when no block is given. Here's why:

1) The form you suggest would be redundant with `Enumerable#to_h` 

2) It would be more powerful, for example to associate things that need an index...

    rng.each_with_index.associate {|elem, index| ....} # => { [elem, index] => ... }, not what you want
    # Easy this form:
    rng.associate.with_index {|elem, index| ... }  # => { elem => ... }

3) Consistency with modern methods dealing with enumerable.


----------------------------------------
Feature #7341: Enumerable#associate
https://bugs.ruby-lang.org/issues/7341#change-32869

Author: nathan.f77 (Nathan Broadbent)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: next minor


Jeremy Kemper proposed Enumerable#associate during the discussion in #7297, with the following details:

-------------------

Some background:

#4151 proposes an Enumerable#categorize API, but it's complex and hard to understand its behavior at a glance.
#7292 proposes an Enumerable#to_h == Hash[...] API, but I don't think of association/pairing as explicit coercion, so #to_h feels misfit.

Associate is a simple verb with unsurprising results. It doesn't introduce ambiguous "map" naming. You associate an enumerable of keys with yielded values.

Some before/after examples:

Before: Hash[ filenames.map { |filename| [ filename, download_url(filename) ]}]
After:  filenames.associate { |filename| download_url filename }
# => {"foo.jpg"=>"http://...", ...}

Before: alphabet.each_with_index.each_with_object({}) { |(letter, index), hash| hash[letter] = index }
After:  alphabet.each_with_index.associate
# => {"a"=>0, "b"=>1, "c"=>2, "d"=>3, "e"=>4, "f"=>5, ...}

Before: keys.each_with_object({}) { |k, hash| hash[k] = self[k] }  # a simple Hash#slice
After:  keys.associate { |key| self[key] }


-------------------

It's worth noting that this would compliment ActiveSupport's Enumerable#index_by method: http://api.rubyonrails.org/classes/Enumerable.html#method-i-index_by
#index_by produces '{<block result> => el, ...}', while #associate would produce '{el => <block result>, ...}'.

For cases where you need to control both keys and values, you could use '[1,2,3].map{|i| [i, i * 2] }.associate', or continue to use 'each_with_object({})'.



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