更新字典中的嵌套计数器

Question

I am going through a large CSV file line by line. What I want to do is count occurrences of the strings in a certain column. Where I am running into trouble is that I would like the counter to be nested inside of a dictionary, where the keys for the outer dictionary is the value from another column. I need to do this or else the data will be processed incorrectly as there are duplicates.

imagine my CSV:

outerDictKey    CounterKey
apple     purple
apple     blue
pear    purple

So basically I want:

dictionary = { apple:
                    counter({blue: 1
                     purple: 1})
                pear:
                   counter({purple: 1})
             }

I wasnt sure how to do this.

myCounter = Counter()
myKey = 'barbara'
counterKey = 'streisand'
largeDict = defaultdict(dict)       
largeDict[myKey] = {myCounter[counterKey] += 1}

Intuitively this looks like it wouldnt work, and of course it gives a syntax error.

I also tried

largeDict[myKey][myCounter][counterKey]+=1

Which throws a "TypeError: unhashable type: 'Counter'" error.

Finally

>>> largeDict[myKey]=Counter()
>>> largeDict[myKey][myCounter][counterKey]+=1

Which still gives a type error. So how do I increment a Counter nested in a dictionary?

Answer 1

This will work:

myCounter = Counter()
largedict = { myKey:
                    {counterKey: myCounter
                     anotherKey: Value2}
             }

largedict[myKey][counterKey]['somethingyouwanttocount']+=1

Counter is just a dict with some extra functionality. However, as a dict, it cannot be a key in a dict, nor an entry in a set, which explains the unhashable exception.

Alternatively, if you're keeping track of information about coherent entities, rather than using nested dicts , you could store the information (including the counter) in objects, and put the objects in a dict as necessary.

If every value is a counter, then just use defaultdict:

from collections import defaultdict, Counter
largedict = defaultdict(Counter)
largedict['apple']['purple']+=1

Answer 2

If you just want to count occurrences of the strings in a certain column , wouldnt this be enough

import collections
data = "Welcome to stack overflow. To give is to get."

print collections.Counter(data.split())

Output

Counter({'to': 2, 'give': 1, 'get.': 1, 'is': 1, 'Welcome': 1, 'To': 1, 'overflow.': 1, 'stack': 1})