How to find the most frequent value in array of hashes - ruby

Question

I have the array of objects "orders". I want to obtain a first most frequent value in the my array, who often takes a book:
orders = [
{'book' => '1', 'reader' => 'Denis' },
{'book' => '2', 'reader' => 'Mike' },
{'book' => '3', 'reader' => 'Denis' },
{'book' => '3', 'reader' => 'Mike' },
{'book' => '5', 'reader' => '2' }
]
I tried this method, but it's good only for arrays of strings: ['string', 'string'...]:
def most_common_value(a)
a.group_by(&:itself).values.max_by(&:size).first
end
Expected result:
=> "Denis"

Answer 1

I'd do it like this:
orders = [
{'book' => '1', 'reader' => 'Denis' },
{'book' => '2', 'reader' => 'Mike' },
{'book' => '3', 'reader' => 'Denis' },
{'book' => '3', 'reader' => 'Mike' },
{'book' => '5', 'reader' => '2' }
]
orders.each_with_object(Hash.new(0)) { |order, hash| hash[order['reader']] += 1 }.max_by { |k, v| v }
# => ["Denis", 2]
The problem with this is, if there are multiple "max" then the result will be returned based on the order the data is found. For instance, if the order is different:
orders.push(orders.shift)
# => [{"book"=>"2", "reader"=>"Mike"},
# {"book"=>"3", "reader"=>"Denis"},
# {"book"=>"3", "reader"=>"Mike"},
# {"book"=>"5", "reader"=>"2"},
# {"book"=>"1", "reader"=>"Denis"}]
the result changes:
orders.each_with_object(Hash.new(0)) { |order, hash| hash[order['reader']] += 1 }.max_by { |k, v| v }
# => ["Mike", 2]

Answer 2

key = 'reader'
x = orders.inject({}) do |a,i|
a[i[key]] = 0 unless a.has_key? i[key]
a[i[key]] +=1
a
end.max_by{|k,v| v}
Which returns:
=> ["Denis", 2]

Answer 3

I saw this a few days ago and thought this would be easy if Array or Enumerable had a mode_by! Well I finally got around to whipping one up.
Implementing mode_by
A true mode_by would probably return a subarray of the items matching a block:
orders.mode_by{|order| order['reader']}
#=> [{'book'=>'1', 'reader'=>'Denis'}, {'book'=>'3', 'reader'=>'Denis'}]
and to get your desired result:
orders.mode_by{|order| order['reader']}.first['reader']
#=> "Denis"
So let's implement a mode_by:
class Array
def mode_by(&block)
self.group_by(&block).values.max_by(&:size)
end
end
et voila!
A custom alternative
In your case, you don't need to return array elements. Let's simplify further by implementing something that returns exactly what you want, the first result of the block that appears the most. We'll call it mode_of:
class Array
def mode_of(&block)
self.group_by(&block).max_by{|k,v| v.size}.first
end
end
Now you can simply do this:
orders.mode_of{|order| order['reader']}
#=> "Denis"

Answer 4

using group_by and max_by :
orders.group_by { |h| h['reader']}.to_a.max_by {|x| x[1].length}.first
Output :
=> "Denis"