[ruby-core:66591] [ruby-trunk - Feature #10552] [PATCH] Add Enumerable#frequencies and Enumerable#relative_frequencies

Issue #10552 has been updated by Robert A. Heiler.


I like the word .frequencies - it seems nicer than each_with_object(Hash.new(0)) and also 
than group_by.

I do not like the word .relative_frequencies but I can understand why you want this - it
seems more a subpart of statistics though, and would perhaps be better placed into some 
extension into ruby (either into math, or perhaps statistics, which could be a 
subproject of ruby math).

On a side-note, perhaps we can also improve on ruby statistics functionality a bit. I'd
rather use Ruby than R, speed difference is no issue for me, but Ruby is much nicer to 
work with than R.

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Feature #10552: [PATCH] Add Enumerable#frequencies and Enumerable#relative_frequencies
https://bugs.ruby-lang.org/issues/10552#change-50207

* Author: Brian Hempel
* Status: Open
* Priority: Normal
* Assignee: 
* Category: core
* Target version: 
----------------------------------------
Counting how many times a value appears in some collection has always been a bit clumsy in Ruby. While Ruby has enough constructs to do it in one line, it still requires knowing the folklore of the optimum solution as well as some acrobatic typing:

~~~ruby
%w[cat bird bird horse].each_with_object(Hash.new(0)) { |word, hash| hash[word] += 1 }
# => {"cat" => 1, "bird" => 2, "horse" => 1}
~~~

What if Ruby could count for us? This patch adds two methods to enumerables:

~~~ruby
%w[cat bird bird horse].frequencies
# => {"bird" => 2, "horse" => 1, "cat" => 1}

%w[cat bird bird horse].relative_frequencies
# => {"bird" => 0.5, "horse" => 0.25, "cat" => 0.25}
~~~

To make programmers happier, the returned hash has the most common values first. This is nice because, for example, finding the most common element of a collection becomes trivial:

~~~ruby
most_common, count = %w[cat bird bird horse].frequencies.first
~~~

Whereas the best you can do with vanilla Ruby is:

~~~ruby
most_common, count = %w[cat bird bird horse].each_with_object(Hash.new(0)) { |word, hash| hash[word] += 1 }.max_by(&:last)

# or...

most_common, count = %w[cat bird bird horse].group_by(&:to_s).map { |word, arr| [word, arr.size] }.max_by(&:last)
~~~

While I don't like the long method names, "frequencies" and "relative frequencies" are the terms used in basic statistics. http://en.wikipedia.org/wiki/Frequency_%28statistics%29


---Files--------------------------------
add_enum_frequencies.patch (5.81 KB)


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