[Tutor] Dictionary - count values where values are stored as a list

[Kent Johnson]

GTXY20 wrote:
> Hello,
> 
> Any way to display the count of the values in a dictionary where the 
> values are stored as a list? here is my dictionary:
> 
> {'1': ['a', 'b', 'c'], '3': ['a', 'b', 'c'], '2': ['a', 'b', 'c'], '4': 
> ['a', 'c']}
> 
> I would like to display count as follows and I would not know all the 
> value types in the values list:
> 
> Value QTY
> a       4
> b       3
> c       4

You need two nested loops - one to loop over the dictionary values and 
one to loop over the individual lists. collections.defaultdict is handy 
for accumulating the counts but you could use a regular dict also:

In [4]: d={'1': ['a', 'b', 'c'], '3': ['a', 'b', 'c'], '2': ['a', 'b', 
'c'], '4': ['a', 'c']}
In [5]: from collections import defaultdict
In [6]: counts=defaultdict(int)
In [7]: for lst in d.values():
    ...:     for item in lst:
    ...:         counts[item] += 1
    ...:
In [8]: counts
Out[8]: defaultdict(<type 'int'>, {'a': 4, 'c': 4, 'b': 3})

In [10]: for k, v in sorted(counts.items()):
    ....:     print k,v
    ....:
    ....:
a 4
b 3
c 4


> Also is there anyway to display the count of the values list 
> combinations so here again is my dictionary:
> 
> {'1': ['a', 'b', 'c'], '3': ['a', 'b', 'c'], '2': ['a', 'b', 'c'], '4': 
> ['a', 'c']}
> 
> 
> And I would like to display as follows
> 
> QTY Value List Combination
> 3      a,b,c
> 1      a,c

Again you can use a defaultdict to accumulate counts. You can't use a 
mutable object (such as a list) as a dict key so you have to convert it 
to a tuple:

In [11]: c2=defaultdict(int)
In [13]: for v in d.values():
    ....:     c2[tuple(v)] += 1
    ....:
In [14]: c2
Out[14]: defaultdict(<type 'int'>, {('a', 'b', 'c'): 3, ('a', 'c'): 1})

Printing in order of count requires switching the order of the (key, 
value) pairs:

In [15]: for count, items in sorted( ((v, k) for k, v in c2.items()), 
reverse=True):
    ....:     print count, ', '.join(items)
    ....:
3 a, b, c
1 a, c

or using a sort key:
In [16]: from operator import itemgetter
In [17]: for items, count in sorted(c2.items(), key=itemgetter(1), 
reverse=True):
    ....:     print count, ', '.join(items)
    ....:
3 a, b, c
1 a, c

Kent