Expanded dictionary inversion in Python (July 11, 2006)

dictionary_inversion.py

# This is actually just a variant of a recipe I posted to ActiveState over five years ago.
# Location: http://code.activestate.com/recipes/496881-expanded-dictionary-inversion/


# the actual code that matters here. first argument must be a dictionary. 
def invert(d, unique=False):
  dd = {}
  for k, v in d.items():
    if not isinstance(v, (tuple, list)): v = [v]
    if unique:
      dd.update( [(vv, dd.setdefault(vv, []) + [k]) for vv in v] )
    else:
      [dd.setdefault(vv, []).append(k) for vv in v]
  return dd
 

# some example dictionaries to test out
def test():
  examples = [
    { 'A': (1,), 'C': (3, 3), 'B': (2, 4) },
    { 'A': [3, 2, 1], 'C': [3, 2], 'B': [1, 4] },
    { 'A': 2, 'C': 4, 'B': 5, 'D': 5 },
    { 'C': (4, 1 , 4, 9), 'B': 5, 'D': [5, 3], 'E': '9' },
    { 'A': [1, 2, 3], 'B': 4 }
  ] 
  for e in examples:
    a = invert(e)
    b = invert(e, 1)
    print '\n'
    print ' original:', x
    print ' inverted:', a
    print ' + unique:', b
    if a!=b:
      print ' ---------> Find the difference!'


### test() will output the following
'''
 original: {'A': [1, 1], 0: 'X', 3: [5, 3], 1: None}
 inverted: {1: ['A'], 2: ['B'], 3: ['C', 'C'], 4: ['B']}
 + unique: {1: ['A'], 2: ['B'], 3: ['C'], 4: ['B']}
 ---------> Find the difference!


 original: {'A': [1, 1], 0: 'X', 3: [5, 3], 1: None}
 inverted: {1: ['A', 'B'], 2: ['A', 'C'], 3: ['A', 'C'], 4: ['B']}
 + unique: {1: ['A', 'B'], 2: ['A', 'C'], 3: ['A', 'C'], 4: ['B']}


 original: {'A': [1, 1], 0: 'X', 3: [5, 3], 1: None}
 inverted: {2: ['A'], 4: ['C'], 5: ['B', 'D']}
 + unique: {2: ['A'], 4: ['C'], 5: ['B', 'D']}


 original: {'A': [1, 1], 0: 'X', 3: [5, 3], 1: None}
 inverted: {1: ['C'], 3: ['D'], 4: ['C', 'C'], 5: ['B', 'D'], 9: ['C'], '9': ['E']}
 + unique: {1: ['C'], 3: ['D'], 4: ['C'], 5: ['B', 'D'], 9: ['C'], '9': ['E']}
 ---------> Find the difference!


 original: {'A': [1, 1], 0: 'X', 3: [5, 3], 1: None}
 inverted: {1: ['A'], 2: ['A'], 3: ['A'], 4: ['B']}
 + unique: {1: ['A'], 2: ['A'], 3: ['A'], 4: ['B']}

'''