Clustering the keys of a dict according to its values

[Florian Brucker]

Wow, thanks everybody! There's a lot to learn for me from these examples...


Enjoy your weekend!
Florian

Florian Brucker wrote:
> Hi everybody!
> 
> Given a dictionary, I want to create a clustered version of it, 
> collecting keys that have the same value:
> 
>  >>> d = {'a':1, 'b':2, 'c':1, 'd':1, 'e':2, 'f':3}
>  >>> cluster(d)
> {1:['a', 'c', 'd'], 2:['b', 'e'], 3:['f']}
> 
> That is, generate a new dict which holds for each value of the old dict 
> a list of the keys of the old dict that have that very value.
> 
> Another requirement is that it should also work on lists, in that case 
> with indices instead of keys. We may assume that all values in the 
> original dict/list can be used as dict keys.
> 
> Right now I'm doing it like this:
> 
>    def cluster(d):
>      try:
>        # is d a dict?
>        values = unique(d.values())
>        keys = d.keys()
>      except AttributeError:
>        # assume d is a list
>        values = unique(d)
>        keys = range(len(d))
> 
>      clusters = {}
>      for value in values:
>        clusters[value] = filter(lambda v: d[v] == value, keys)
> 
>      return clusters
> 
> where unique() is from O'Reilly's Python Cookbook and returns a list 
> containing each item of the given list exactly once.
> 
> Now I'm pretty new to Python and chances are rather high that this could 
> be done prettier and/or more efficient. Therefore any comment on the 
> above code is greatly appreciated.
> 
> 
> Regards,
> Florian