Question

我有一个由制表符分隔的文本文件（data.txt），如下所示：

name    height  weight
A   15.5    55.7
B   18.9    51.6
C   17.4    67.3
D   11.4    34.5
E   23.4    92.1

下面的程序将结果作为字符串列表。

with open('data.txt', 'r') as f:
    col1 = [line.split()[0] for line in f]
    data1 = col1 [1:]
    print (data1)
with open('data.txt', 'r') as f:
    col2 = [line.split()[1] for line in f]
    data2 = col2 [1:]
    print (data2)
with open('data.txt', 'r') as f: 
    col3 = [line.split()[2] for line in f]
    data3 = col3 [1:]
    print (data3)

结果如下：

['A', 'B', 'C', 'D', 'E']
['15.5', '18.9', '17.4', '11.4', '23.4']
['55.7', '51.6', '67.3', '34.5', '92.1']

但是，我想将data2和data3作为浮点数列表。我该如何纠正以上程序？请帮忙。

Answer 1

这里不需要读取文件3次，你可以通过定义一个简单的函数来做到这一点，如果它是一个有效的数字，则返回该项的浮点值，否则按原样返回。

现在使用列表推导逐个读取所有行，并将此函数应用于每行的项目。现在您已经有了一个列表列表，现在是时候使用zip(*)解压缩该列表列表，并将返回值分配给data1，data2，data3

def ret_float(x):
    try:
        return float(x)
    except ValueError:
        return x

with open('data.txt') as f:
    next(f) #skip the header
    lis = [ map(ret_float,line.split()) for line in f]
    #[['A', 15.5, 55.7], ['B', 18.9, 51.6], ['C', 17.4, 67.3], ['D', 11.4, 34.5], ['E', 23.4, 92.1]]
    #unzip the list
    data1, data2, data3 = zip(*lis)

    #if you want data1,data2,data3 to be lists then use:
    #data1, data2, data3 = [list(x) for x in  zip(*lis)]
...     
>>> data1
('A', 'B', 'C', 'D', 'E')
>>> data2
(15.5, 18.9, 17.4, 11.4, 23.4)
>>> data3
(55.7, 51.6, 67.3, 34.5, 92.1)

更新：修复解决方案

with open('data.txt', 'r') as f:
    col2 = [line.split()[1] for line in f]
    data2 = list(map(float, col2 [1:]))   # apply float to each item using `map`
                                          # as `map` returns a `map` object in py3.x
                                          # you have to pass it to list() 
with open('data.txt', 'r') as f: 
    col3 = [line.split()[2] for line in f]
    data3 = list(map(float, col3 [1:]))
    print (data3)

map上的

帮助：

>>> print(map.__doc__)
map(func, *iterables) --> map object

Make an iterator that computes the function using arguments from
each of the iterables.  Stops when the shortest iterable is exhausted.

Answer 2

使用float()功能。它需要1个arg，这将是你想要变成浮点数的字符串/ var。

Answer 3

使用float()命令：

with open('data.txt', 'r') as f:
    col2 = [float(line.split()[1]) for line in f]
    data2 = col2[1:]
    print(data2)

Answer 4

在阅读时将字符串转换为float：

data1 = col1 [1:]

变为

data1 = float(col1 [1:])

但是 - 我知道你没有问过这个问题 - 你的做法有点侧面。您可能想要考虑更像这样的程序结构：

data0 = []
data1 = []
data2 = []
with open('data.txt', 'r') as f:
    f.readline()
    for line in f:
        vals = line.split()
        data0.append(vals[0])
        data1.append(vals[1])
        data2.append(vals[2])
print(data0)
print(data1)
print(data2)

希望它有所帮助！

（免责声明：适用于Python 2.7;不确定3.x。）

Answer 5

with open('data.txt', 'r') as f:
    col1 = [line.split()[0] for line in f]
    data1 = col1 [1:]
    print (data1)
with open('data.txt', 'r') as f:
    col2 = [line.split()[1] for line in f]
    data2 = float(col2 [1:])
    print (data2)
with open('data.txt', 'r') as f: 
    col3 = [line.split()[2] for line in f]
    data3 = float(col3 [1:])
    print (data3)

从字符串列表到浮动列表

5 个答案: