Updating a dictionary

Question

I have created three dictionaries-dict1, dict2, and dict2. I want to update dict1 with dict2 first, and resulting dictionary with dict3. I am not sure why they are not adding up.

def wordcount_directory(directory):
    dict = {}
    filelist=[os.path.join(directory,f) for f in os.listdir(directory)]
    dicts=[wordcount_file(file) for file in filelist]
    dict1=dicts[0]
    dict2=dicts[1]
    dict3=dicts[2]
    for k,v in dict1.iteritems():
        if k in dict2.keys():
            dict1[k]+=1
        else:
            dict1[k]=v
    for k1,v1 in dict1.iteritems():
        if k1 in dict3.keys():
            dict1[k1]+=1
        else:
            dict1[k1]=v1
return dict1

print wordcount_directory("C:\\Users\\Phil2040\\Desktop\\Word_count")  

Answer 1

Maybe I am not understanding you question right, but are you trying to add all the values from each of the dictionaries together into one final dictionary? If so:

dict1 = {'a': 1, 'b': 2, 'c': 3}
dict2 = {'b': 5, 'c': 1, 'd': 9}
dict3 = {'d': 1, 'e': 7}

def add_dict(to_dict, from_dict):
    for key, value in from_dict.iteritems():
        to_dict[key] = to_dict.get(key, 0) + value

result = dict(dict1)
add_dict(result, dict2)
add_dict(result, dict3)
print result

This yields: {'a': 1, 'c': 4, 'b': 7, 'e': 7, 'd': 10}

It would be really helpful to post what the expected outcome should be for your question.

EDIT:

For an arbitrary amount of dictionaries:

result = dict(dicts[0])
for dict_sum in dicts[1:]:
    add_dict(result, dict_sum)
print(result)

If you really want to fix the code from your original question in the format it is in:

1. You are using dict1[k]+=1 when you should be performing dict1[k]+=dict2.get(k, 0).
2. The introduction of get removes the need to check for its existence with an if statement.
3. You need to iterate though dict2 and dict3 to introduce new keys from them into dict1
4. (not really a problem, but worth mentioning) In the if statement to check if the key is in the dictionary, it is recommended to simply the operation to if k in dict2: (see this post for more details)

With the amazing built-in library found by @DisplacedAussie, the answer can be simplified even further:

from collections import Counter

print(Counter(dict1) + Counter(dict2) + Counter(dict3))

The result yields: Counter({'d': 10, 'b': 7, 'e': 7, 'c': 4, 'a': 1})

The Counter object is a sub-class of dict, so it can be used in the same way as a standard dict.

Answer 2

Hmmm, here a simple function that might help:

def dictsum(dict1, dict2):
   '''Modify dict1 to accumulate new sums from dict2
   '''
   k1 = set(dict1.keys())
   k2 = set(dict2.keys())
   for i in k1 & k2:
       dict1[i] += dict2[i]
   for i in k2 - k1:
       dict1[i] = dict2[i]
   return None

... for the intersection update each by adding the second value to the existing one; then for the difference add those key/value pairs.

With that defined you'd simple call:

dictsum(dict1, dict2)
dictsum(dict1, dict3)

... and be happy.

(I will note that functions modify the contents of dictionaries in this fashion are not all that common. I'm returning None explicitly to follow the convention established by the list.sort() method ... functions which modify the contents of a container, in Python, do not normally return copies of the container).

Answer 3

If I understand your question correctly, you are iterating on the wrong dictionary. You want to iterate over dict2 and update dict1 with matching keys or add non-matching keys to dict1.

If so, here's how you need to update the for loops:

for k,v in dict2.iteritems():     # Iterate over dict2
    if k in dict1.keys():         
        dict1[k]+=1               # Update dict1 for matching keys 
    else:
        dict1[k]=v                # Add non-matching keys to dict1
for k1,v1 in dict3.iteritems():   # Iterate over dict3
    if k1 in dict1.keys():
        dict1[k1]+=1              # Update dict1 for matching keys
    else:
        dict1[k1]=v1              # Add non-matching keys to dict1

Answer 4

I assume that wordcount_file(file) returns a dict of the words found in file, with each key being a word and the associated value being the count for that word. If so, your updating algorithm is wrong. You should do something like this:

keys1 = dict1.keys()
for k,v in dict2.iteritems():
    if k in keys1:
        dict1[k] += v
    else:
        dict1[k] = v

If there's a lot of data in these dicts you can make the key lookup faster by storing the keys in a set:

keys1 = set(dict1.keys())

You should probably put that code into a function, so you don't need to duplicate the code when you want to update dict1 with the data in dict3.

You should take a look at collections.Counter, a subclass of dict that supports counting; using Counters would simplify this task considerably. But if this is an assignment (or you're using Python 2.6 or older) you may not be able to use Counters.