CODEWITHSUNDEEP
pythonlistdictionarycountpython-3.3
RolfBly
RolfBly

Reputation: 3862

Python count items in dict value that is a list

Python 3.3, a dictionary with key-value pairs in this form. 

d = {'T1': ['eggs', 'bacon', 'sausage']}

The values are lists of variable length, and I need to iterate over the list items. This works: 

count = 0
for l in d.values():
   for i in l: count += 1

But it's ugly. There must be a more Pythonic way, but I can't seem to find it.

len(d.values())

produces 1. It's 1 list (DUH). Attempts with Counter from here give 'unhashable type' errors.

Upvotes: 18

Views: 68361

Answers (5)

mluanastevens
mluanastevens

Reputation: 3

For me the simplest way is:

winners = {1931: ['Norman Taurog'], 1932: ['Frank Borzage'], 1933: ['Frank Lloyd'], 1934: ['Frank Capra']}

win_count_dict = {}

for k,v in winners.items():
    for winner in v:
        if winner not in win_count_dict:
            win_count_dict[winner]=1
        else:
            win_count_dict[winner]+=1


print("win_count_dict = {}".format(win_count_dict))

Upvotes: 0

Rik Schoonbeek
Rik Schoonbeek

Reputation: 4450

Doing my homework on Treehouse I came up with this. It can be made simpler by one step at least (that I know of), but it might be easier for beginners (like myself) to onderstand this version.

dict = {'T1': ['eggs', 'bacon', 'sausage'], 'T2': ['bread', 'butter', 'tosti']}

total = 0

for value in dict:
    value_list = dict[value]
    count = len(value_list)
    total += count

print(total)

Upvotes: 0

Jeffrey
Jeffrey

Reputation: 105

I was looking for an answer to this when I found this topic untill I realized I already had something in my code to use this for. This is what I came up with:

count = 0

for key, values in dictionary.items():
        count = len(values)

If you want to save the count for every dictionary item you could create a new dictionary to save the count for each key.

count = {}

for key, values in dictionary.items():
        count[key] = len(values)

I couldn't exactly find from which version this method is available but I think .items method is only available in Python 3.

Upvotes: -1

Martijn Pieters
Martijn Pieters

Reputation: 1121494

Use sum() and the lengths of each of the dictionary values:

count = sum(len(v) for v in d.itervalues())

If you are using Python 3, then just use d.values().

Quick demo with your input sample and one of mine:

>>> d = {'T1': ['eggs', 'bacon', 'sausage']}
>>> sum(len(v) for v in d.itervalues())
3
>>> d = {'T1': ['eggs', 'bacon', 'sausage'], 'T2': ['spam', 'ham', 'monty', 'python']}
>>> sum(len(v) for v in d.itervalues())
7

A Counter won't help you much here, you are not creating a count per entry, you are calculating the total length of all your values.

Upvotes: 52

John La Rooy
John La Rooy

Reputation: 304137

>>> d = {'T1': ['eggs', 'bacon', 'sausage'], 'T2': ['spam', 'ham', 'monty', 'python']}
>>> sum(map(len, d.values()))
7

Upvotes: 16

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