Grouping consecutive numbers in an array

Question

I need to add consecutive numbers to a new array and, if it is not a consecutive number, add only that value to a new array:

old_array = [1, 2, 3, 5, 7, 8, 9, 20, 21, 23, 29]

I want to get this result:

 new_array = [
  [1,2,3],
  [5],
  [7,8,9]
  [20,21]
  [23],
  [29]
]

Is there an easier way to do this？

Answer 1

A little late to this party but:

old_array.slice_when { |prev, curr| curr != prev.next }.to_a
# => [[1, 2, 3], [5], [7, 8, 9], [20, 21], [23], [29]]

Answer 2

This is the official answer given in RDoc (slightly modified):

actual = old_array.first
old_array.slice_before do
  |e|
  expected, actual = actual.next, e
  expected != actual
end.to_a

Answer 3

A couple other ways:

old_array = [1, 2, 3, 5, 7, 8, 9, 20, 21, 23, 29]

#1

a, b = [], []
enum = old_array.each
loop do
  b << enum.next
  unless enum.peek.eql?(b.last.succ)
    a << b
    b = []
  end
end
a << b if b.any?
a #=> [[1, 2, 3], [5], [7, 8, 9], [20, 21], [23], [29]]

#2

def pull_range(arr)
  b = arr.take_while.with_index { |e,i| e-i == arr.first }
  [b, arr[b.size..-1]]
end

b, l = [], a
while l.any?
  f, l = pull_range(l)
  b << f
end
b #=> [[1, 2, 3], [5], [7, 8, 9], [20, 21], [23], [29]]