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Feature #7341

Enumerable#associate

Added by nathan.f77 (Nathan Broadbent) over 7 years ago. Updated over 2 years ago.

Status:
Open
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:49268]

Description

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 '{ => el, ...}', while #associate would produce '{el => , ...}'.

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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