Group Users by Age Range in ruby

Question

I\'m trying to list the number of users by age-range:

Range  : #Users
10-14  : 16
15-21  : 120
22-29  : 312
30-40  : 12131
41-70  : 612
71-120 : 20
         


        

Answer 1

I find the accepted answer to be a bit dense. Fast but hard to understand and write. Today, I came up with a slower but simpler solution. Since we are grouping ages into ranges, we can assume that we won't have values over 125

That means that if you use a ruby filter on a grouped and counted result set, you won't iterate over more than 125 items. This will be slower than a sql range based group/count, but it was fast enough for my purposes while still relying on the DB for most of the heavy lifting. Iterating over a hash with less than 125 items doesn't seem like a big deal. Especially when the key value pairs are just ints like this:

{
  0 => 0,
  1 => 1,
  3 => 5,
  25 => 3,
  99 => 3
}

Here's the psudo-code:

users = User
  .where(age: (min..max))
  .group(:age)
  .count(:age)
group = Hash.new(0)
users.each{|age, count|
      case
      when age <= 10
        group['under 10'] += count
      when age <= 25
        group['11-25'] += count
      when age <= 40
        group['26-40'] += count
      else
        group['41+'] += count
      end
}

Note: this solution provides the count of users in a given range.