Reorganize basic list into nested lists, with similar elements per level.

nest.py

# 2012.11.11 - 02:44:45
# (Python 3.3)
def nest(bird):
  """Recursively nest similar elements at same level."""
  if not bird: return []
  beak = bird[0] # Current element to match for this level.
  egg = []

  prev = 0
  while beak in bird:
    next = bird.index(beak)
    # Jump to relevant index and update context.
    if next > prev:
      egg += [nest(bird[prev:next])]
    egg += [bird[next]]
    bird = bird[next+1:]
  # Trailing non-similars.
  if prev < len(bird):  egg += [bird[prev:]]

  return egg

test = [1,2,3,3,4,4,2,1]
print(nest(test))   # [1, [2, [3, 3, [4, 4]], 2], 1]

Re: https://twitter.com/ftrain/status/267503513477713920