Hi all,

I've run into a number of situations where I need to group an array
while preserving order. For example, grouping the results of a database
query without affecting their order or introducing extraneous logic in a
view.

I would like to know if there are any obvious problems or improvements
to this solution:

class Array
  def partition_by(&b)
    out=[]
    self.inject([]) {|acc,e|
      last = acc.pop
      value = b.call(e)
      out << {value=>[]} if last != value
      out.last[value] << e
      acc << value
    }
    out
  end
end

So if I partition an array by element length, for example (contrived, I
know):
animals = %w(dog dog cat chicken chicken dog)
animals.partition_by{|x| x.length}

I get:
[{3=>["dog", "dog", "cat"]}, {7=>["chicken", "chicken"]}, {3=>["dog"]}]

Any thoughts or suggestions?

- Matt
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