计算元组列表中的出现次数

Question

I am fairly new to python, but I haven't been able to find a solution to my problem anywhere.

I want to count the occurrences of a string inside a list of tuples.

Here is the list of tuples:

list1 = [
         ('12392', 'some string', 'some other string'),
         ('12392', 'some new string', 'some other string'),
         ('7862', None, 'some other string')
        ]

I've tried this but it just prints 0

for entry in list1:
    print list1.count(entry[0])

As the same ID occurs twice in the list, this should return:

2
1

I also tried to increment a counter for each occurrence of the same ID but couldn't quite grasp how to write it.

*EDIT: Using Eumiro's awesome answer. I just realized that I didn't explain the whole problem. I actually need the total amount of entries which has a value more than 1. But if I try doing:

for name, value in list1:

    if value > 1:
        print value

I get this error:

ValueError: Too many values to unpack

Answer 1

Maybe collections.Counter could solve your problem:

from collections import Counter
Counter(elem[0] for elem in list1)

returns

Counter({'12392': 2, '7862': 1})

It is fast since it iterates over your list just once. You iterate over entries and then try to get a count of these entries within your list. That cannot be done with .count , but might be done as follows:

for entry in list1:
    print sum(1 for elem in list1 if elem[0] == entry[0])

But seriously, have a look at collections.Counter .

EDIT : I actually need the total amount of entries which has a value more than 1.

You can still use the Counter :

c = Counter(elem[0] for elem in list1)
sum(v for k, v in c.iteritems() if v > 1)

returns 2 , ie the sum of counts that are higher than 1.

Answer 2

list1.count(entry[0]) will not work because it looks at each of the three tuples in list1 , eg. ('12392', 'some string', 'some other string') and checks if they are equal to '12392' for example, which is obviously not the case.

@eurmiro's answer shows you how to do it with Counter (which is the best way!) but here is a poor man's version to illustrate how Counter works using a dictionary and the dict.get(k, [,d]) method which will attempt to get a key ( k ), but if it doesn't exist it returns the default value instead ( d ):

>>> list1 = [
         ('12392', 'some string', 'some other string'),
         ('12392', 'some new string', 'some other string'),
         ('7862', None, 'some other string')
]
>>> d = {}
>>> for x, y, z in list1:
        d[x] = d.get(x, 0) + 1


>>> d
{'12392': 2, '7862': 1}

Answer 3

I needed some extra functionality that Counter didn't have. I have a list of tuples that the first element is the key and the second element is the amount to add. @jamylak solution was a great adaptation for this!

>>> list = [(0,5), (3,2), (2,1), (0,2), (3,4)]

>>> d = {}
>>> for x, y in list1:
    d[x] = d.get(x, 0) + y

>>> d
{0: 7, 2: 1, 3: 6}