问题
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
回答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
, i.e. the sum of counts that are higher than 1.
回答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}
回答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}
来源:https://stackoverflow.com/questions/16013485/counting-the-amount-of-occurrences-in-a-list-of-tuples