count the number of occurrences of a certain value in a dictionary in python?

问题

If I have got something like this:

D = {'a': 97, 'c': 0 , 'b':0,'e': 94, 'r': 97 , 'g':0}

If I want for example to count the number of occurrences for the "0" as a value without having to iterate the whole list, is that even possible and how?

回答1:

As I mentioned in comments you can use a generator within sum() function like following:

sum(value == 0 for value in D.values())

Or as a slightly more optimized and functional approach you can use map function as following:

sum(map((0).__eq__, D.values()))

Benchmark:

In [56]: %timeit sum(map((0).__eq__, D.values()))
1000000 loops, best of 3: 756 ns per loop

In [57]: %timeit sum(value == 0 for value in D.values())
1000000 loops, best of 3: 977 ns per loop

Note that although using map function in this case may be more optimized but in order to achieve a comprehensive and general idea about the two approaches you should run the benchmark for relatively large datasets as well. Then you can decide when to use which in order to gain the more performance.

回答2:

Alternatively, using collections.Counter:

from collections import Counter
D = {'a': 97, 'c': 0 , 'b':0,'e': 94, 'r': 97 , 'g':0}

Counter(D.values())[0]
# 3

回答3:

You can count it converting it to a list as follows:

D = {'a': 97, 'c': 0 , 'b':0,'e': 94, 'r': 97 , 'g':0}
print(list(D.values()).count(0))
>>3

Or iterating over the values:

print(sum([1 for i in D.values() if i == 0]))
>>3

来源：https://stackoverflow.com/questions/48371856/count-the-number-of-occurrences-of-a-certain-value-in-a-dictionary-in-python