Splitting an array into sub arrays 2 - ruby-on-rails

Question

This question follows on from a similar question I asked previously:
Splitting an array into sub arrays
I have been struggling with this code for a while now. I have an array of data "master" with each element having a lft & rgt value. I wish to break this "master" array in to an array of sub arrays "groups". The desired groupings of these sub arrays is illustrated below.
The trigger to create a new sub array is where the lft value is not between the lft & rgt values of the first elemenet in the array.
My thinking was to:
a) initialise the first array then loop through the remaining elements.
b) Check the element's lft value against the lft & rgt values of the first element in the last sub array.
c) if out side the range then create a new sub array
d) append the element onto the last sub array.
when I try this I recive an error for a unknown method "new"
def display_visiting
groups = []
master = []
master << { id: 1, name: "Fred", lft: 1, rgt: 4 }
master << { id: 4, name: "Sue", lft: 2, rgt: 3 }
master << { id: 2, name: "May", lft: 5, rgt: 12 }
master << { id: 5, name: "Helen", lft: 6, rgt: 7 }
master << { id: 6, name: "Peter", lft: 8, rgt: 9 }
master << { id: 7, name: "Grace", lft: 10, rgt: 11 }
master << { id: 3, name: "Brian", lft: 13, rgt: 18 }
master << { id: 8, name: "Michael", lft: 14, rgt: 15 }
master << { id: 9, name: "Paul", lft: 16, rgt: 17 }
groups[0] = master.shift(1)
master.each do |employee|
if (employee.lft < groups.last.first.lft) or (employee.lft > groups.last.first.rgt)
groups.new
end
groups.last << employee
end
return groups
else
return nil
end

Answer 1

new is a Class method used to create a new instance of a Class. E.g an object. groups is an instance of the Array class which is why it doesn't have a new method. If you're not too familiar with class methods vs instance methods, checkout this article.
So if you wanted to add a new Array to the end of the groups array, you would change this:
groups.new
To this:
groups << Array.new
However, you can use the Array initialization shorthand exactly like how you initialized the master array:
groups << []