Question

I am a Ruby Rails newbie.

Is there a way to know the popularity of elements in an Array over time?

For example lets say for the last 15 min..

The array has like [“abc”, “ab”, “abc”, “a”, “abc”, “ab”……..] being pushed into the array.. can we get “abc” and “ab” as the most popular ones.. just for the last 15 minutes?

If you take for an entire hour.. typical for the entire hour..”abcd” is the most popular.. it should return “abcd” as the most popular element in an array..

Is there a way to achieve this?

Answer 1

Create your own class which inherits from Array, or delegates all its functionality to an Array. For example:

class TimestampedArray
  def initialize
    @items = []
  end

  def <<(obj)
    @items << [Time.now,obj]
  end

  # get all the items which were added in the last "seconds" seconds
  # assumes that items are kept in order of add time
  def all_from_last(seconds)
    go_back_to = Time.now - seconds
    result     = []
    @items.reverse_each do |(time,item)|
      break if time < go_back_to
      result.unshift(item)
    end
    result
  end
end

If you have an old version of Ruby, which doesn’t have reverse_each:

def all_from_last(seconds)
  go_back_to = Time.now - seconds
  result     = []
  (@items.length-1).downto(0) do |i|
    time,item = @items[i]
    break if time < go_back_to
    result.unshift(item)
  end
  result
end

Then you need something to find the “most popular” item. I often use this utility function:

module Enumerable
  def to_histogram
    result = Hash.new(0)
    each { |x| result[x] += 1 }
    result
  end
end

On which you could base:

module Enumerable
  def most_popular
    h = self.to_histogram
    max_by { |x| h[x] }
  end
end

So then you get:

timestamped_array.all_from_last(3600).most_popular # "most popular" in last 1 hour