Python：计数器输出上的计数元素

Question

I have a nested list as:

 List1 = [[A,B,A,A],[C,C,B,B],[A,C,B,B]]..... so on

I used counter function to count the number of elements in the nested lists:

for i,j in enumerate(List1):
    print(Counter(j))

I got following output as:

Counter({'A': 3, 'B': 1})
Counter({'C': 2, 'B': 2})
Counter({'B': 2, 'A': 1, 'C': 1})
....

I want to calculate percentage of A in Counter output:

A = number of A's / total number of elements

For example:

Counter({'A': 3, 'B': 1})

Would yield:

A = 3/4 = 0.75

I am not able to calculate A, Can anyone kindly help me with this?

Answer 1

>>> for sublist in List1:
        c = Counter(sublist)
        print(c['A'] / sum(c.values()))

0.75
0.0
0.25

---

All values at once:

>>> for sublist in List1:
        c = Counter(sublist)
        s = sum(c.values())
        print(c['A'] / s, c['B'] / s, c['C'] / s)

0.75 0.25 0.0
0.0 0.5 0.5
0.25 0.5 0.25

If you want to get a list of all items in a sublist with their respective percentages, you need to iterate the counter:

>>> for sublist in List1:
        c = Counter(sublist)
        s = sum(c.values())
        for elem, count in c.items():
            print(elem, count / s)
        print()

A 0.75
B 0.25

B 0.5
C 0.5

A 0.25
B 0.5
C 0.25

Or use a dictionary comprehension:

>>> for sublist in List1:
        c = Counter(sublist)
        s = sum(c.values())
        print({ elem: count / s for elem, count in c.items() })

{'A': 0.75, 'B': 0.25}
{'B': 0.5, 'C': 0.5}
{'A': 0.25, 'B': 0.5, 'C': 0.25}

Answer 2

This:

In [1]: l = [['A','B','A','A'],['C','C','B','B'],['A','C','B','B']]

In [2]: [{i: x.count(i)/float(len(x)) for i in x} for x in l]
Out[2]:
[{'A': 0.75, 'B': 0.25},
 {'B': 0.5, 'C': 0.5},
 {'A': 0.25, 'B': 0.5, 'C': 0.25}]

Answer 3

The following would give you a list of dictionaries holding both the counts and the percentages for each entry:

List1 = [['A','B','A','A'],['C','C','B','B'],['A','C','B','B']]
counts = [Counter(x) for x in List1]
percentages = [{k : (v, v / float(len(l1))) for k,v in cc.items()} for l1, cc in zip(List1, counts)]

print percentages

Giving the following output:

[{'A': (3, 0.75), 'B': (1, 0.25)}, {'C': (2, 0.5), 'B': (2, 0.5)}, {'A': (1, 0.25), 'C': (1, 0.25), 'B': (2, 0.5)}]

For just the percentages:

List1 = [['A','B','A','A'],['C','C','B','B'],['A','C','B','B']]
counts = [Counter(x) for x in List1]
percentages = [{k : v / float(len(l1)) for k,v in cc.items()} for l1, cc in zip(List1, counts)]

print percentages

Giving:

[{'A': 0.75, 'B': 0.25}, {'C': 0.5, 'B': 0.5}, {'A': 0.25, 'C': 0.25, 'B': 0.5}]

Answer 4

You can use list generator and join method to connect your lists of lists of chars into one-liner list of strings.

>>> List1 = [['A', 'B', 'A', 'A'],['C', 'C', 'B', 'B'],['A', 'C', 'B', 'B']]
>>> [''.join(x) for x in List1]
['ABAA', 'CCBB', 'ACBB']

Then, join again your list to the one string.

>>> ''.join(['ABAA', 'CCBB', 'ACBB'])
'ABAACCBBACBB'

And count 'A' symbol, or any other.

>>> 'ABAACCBBACBB'.count('A')
4

This could be one-liner solution:

>>> ''.join(''.join(x) for x in List1).count('A')
4

String of symbols is iterable type. The same as the list. List of strings is more useful than the list of lists of chars.