在Python中从文本文件计算平均值

Question

我有一个文本文件，里面有一串数字。现在我想计算每三组数字的平均值。有没有什么好主意可以做到这一点？谢谢！

文本文件中的数字示例：

5
7
3
10
12
6

我想要的输出结果：

5
9

Answer 1

data.txt:

5
7
3
10
12
6

如何使用 numpy 来处理它：

In [4]: import numpy as np

In [5]: with open('data.txt') as f:
    data = f.read().split()
   ...:     

In [6]: data
Out[6]: ['5', '7', '3', '10', '12', '6']

In [7]: a = np.array(map(float, data))

In [8]: a
Out[8]: array([  5.,   7.,   3.,  10.,  12.,   6.])

In [9]: b = a.reshape([-1,3])

In [10]: b
Out[10]: 
array([[  5.,   7.,   3.],
       [ 10.,  12.,   6.]])

In [11]: b.sum(1)/3
Out[11]: array([ 5.        ,  9.33333333])

Answer 2

你需要“解析”这个文本文件，为了做到这一点，你需要了解它是怎么组织的，以及它是用什么编码的。在此之前，我有几个问题想问你。

1. 这些数字之间会一直有空格吗？
2. 你希望输出结果在哪里？是打印到控制台上，还是放在一个新的文本文件里？

你可以这样做：

#read the file 
my_file = open("C:/numbers.txt",'r')
my_text = my_file.read()
my_file.close()

#get a list of numbers from it (in string form)
my_text_numbers = my_text.split(' ')

#use list comprehension to get integer...also consider
#using map function
my_int_numbers = [int(n) for n in my_text_numbers]

#now the averaging part I will leave to you, I assume it's
#the file reading part you needed help with.

Answer 3

假设每一行都是单独的一行：

# text file is myData.txt
averages = {} # using a dictionary so you can keep track of the starting point
with open('myData.txt', 'r') as myFile:
    data = myFile.read().split('\n') # this creates a list of the data
for index in range(len(data), 3): # step of 3
    n = float(int(data[index]) + int(data[index+1]) + int(data[index+2])) / 3
    averages[index] = n

如果列表的内容不是正好每三项一组，这段代码会出现一个叫做 IndexError 的错误。所以我加上了 try 和 except 这两个部分来处理这个问题：

# text file is myData.txt
averages = {}
with open('myData.txt', 'r') as myFile:
    data = myFile.read().split('\n') # this creates a list of the data
for index in range(len(data), 3): # step of 3
    try: a = int(data[index])
    except (IndexError, TypeError): a = 0
    try: b = int(data[index+1])
    except (IndexError, TypeError): b = 0
    try: c = int(data[index+2])
    except (IndexError, TypeError): c = 0
    # except (IndexError, TypeError): avoids an error if the end of the list 
    # has been reached or the line is not an integer
    n = float(a + b + c) / 3
    averages[index] = n