Python，概率

Question

我的代码如下：

with open("test.txt") as f_in:
    for line in f_in:
        for char in line:
            frequencies[char] += 1

list= [(count, char) for char, count in frequencies.iteritems()]

这段代码打开了test.txt文件，读取每一行，并把每个字符的数量列出来，格式像这样：[(3, 'a'),.........]。这表示在整个文本文件中，有三个'a'，依此类推……

我需要做的是计算这个数字，不是3，而是[ 3 / 所有字符的总数 ]。所以我不需要知道'a'在文本中出现了多少次，而是需要计算'a'的概率。

举个例子，如果在文本(test.txt)中有"aaab"，我想要的输出结果是一个列表：[(0.75, 'a'), (0.25, 'b')]

非常感谢你的帮助。

---

编辑2

import collections
frequencies = collections.defaultdict(int)



with open("test.txt") as f_in:
    for line in f_in:
        for char in line:
            frequencies[char] += 1
total = float(sum(frequencies.keys()))

verj= [(count/total, char) for char, count in frequencies.iteritems()]

这个代码不工作，给我报错：

total = float(sum(frequencies.keys()))

TypeError: unsupported operand type(s) for +: 'int' and 'str'

Answer 1

快速简单：

   counter = 0
   with open("test.txt") as f_in:
        for line in f_in:
            for char in line:
                frequencies[char] += 1
                counter += 1

    list= [(count / counter, char) for char, count in frequencies.iteritems()]

Answer 2

你快到了。

with open("test.txt") as f_in:
    for line in f_in:
        for char in line:
            frequencies[char] += 1
total = float(sum(frequencies.values()))
symbols = [(count/total, char) for char, count in frequencies.iteritems()]

注意，我把你得到的列表改了个名字，因为 list 是一个内置的名称，不应该用来给变量或函数命名。

Answer 3

如果 frequencies = {"a": 3, "b": 4}，那么 frequencies.values() 会给我们 [3, 4]，我们可以计算它们的总和：

total = float(sum(frequencies.values()))

然后我们可以计算概率：

probs = [(count / total, char) for char, count in frequencies.iteritems()]

注意，Python在用两个整数相除时会返回一个整数，这就是我先把总和转换成浮点数的原因：

Python 2.7 (r27:82508, Jul  3 2010, 21:12:11) 
[GCC 4.0.1 (Apple Inc. build 5493)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 3 / 4
0
>>> 3 / 4.0
0.75