Counter for items in lists in lists?

Steven Bethard steven.bethard at gmail.com
Sat Sep 25 09:09:06 CEST 2004


Bryan <belred1 <at> yahoo.com> writes:
> or maybe a less general approach might work if the nested list is always one 
> deep:
> 
>  >>> myList=[['a','b','c','d'],['a','f','g','h'],['a','b','x','y']]
>  >>> tmp = []
>  >>> d = {}
>  >>> for item in myList: tmp += item
>  >>> for key in tmp: d[key] = d.get(key, 0) + 1
>  >>> d
> {'a': 3, 'c': 1, 'b': 2, 'd': 1, 'g': 1, 'f': 1, 'h': 1, 'y': 1, 'x': 1}

Yeah, if that's the case, you don't really even need to construct a temporary 
list:

>>> myList=[['a','b','c','d'],['a','f','g','h'],['a','b','x','y']] 
>>> counts = {}
>>> for lst in myList:
... 	for item in lst:
... 		counts[item] = counts.get(item, 0) + 1
... 		
>>> counts
{'a': 3, 'c': 1, 'b': 2, 'd': 1, 'g': 1, 'f': 1, 'h': 1, 'y': 1, 'x': 1}

Steve




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