从字符串列表到浮点列表

Question

我有一个用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给出。

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，我想获取data2和data3作为浮动列表。 我该如何纠正以上程序？ 请帮忙。

Answer 1

此处无需读取文件3次，您可以通过定义一个简单函数来实现此目的，如果该函数是有效数字，则该函数将返回该项目的浮点值，否则将按原样返回。

现在，使用列表理解一一读取所有行，并将此功能应用于每一行的项目。 因此，现在您有了一个列表列表，是时候使用zip(*)解压缩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 ：解决您的问题

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 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()函数。 它需要1个arg，它将是您想要转换为浮点型的字符串/ 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

读取时将字符串转换为float ：

data1 = col1 [1:]

变成

data1 = float(col1 [1:])

---

但是-我知道您没有问这个-您的方法有点偏斜。 您可能想考虑一个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)

希望能帮助到你！

（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)