差异

Question

可能重复：
Python - Differences between elements of a list

我有一个名单，我想找到连续元素之间的区别：

a = [0, 4, 10, 100] 
find_diff(a) 
>>> [4,6,90] 

将如何你的代码find_diff（）函数？我可以用“for”迭代器编写这个代码，但我确信有一个简单的方法可以用一个简单的一行代码来完成。

Answer 1

你可以利用enumerate，zip和list comprehensions：

>>> a = [0, 4, 10, 100] 

# basic enumerate without condition: 
>>> [x - a[i - 1] for i, x in enumerate(a)][1:] 
[4, 6, 90] 

# enumerate with conditional inside the list comprehension: 
>>> [x - a[i - 1] for i, x in enumerate(a) if i > 0] 
[4, 6, 90] 

# the zip version seems more concise and elegant: 
>>> [t - s for s, t in zip(a, a[1:])] 
[4, 6, 90] 

性能的角度来看，似乎是没有太多的差异：

In [5]: %timeit [x - a[i - 1] for i, x in enumerate(a)][1:] 
1000000 loops, best of 3: 1.34 µs per loop 

In [6]: %timeit [x - a[i - 1] for i, x in enumerate(a) if i > 0] 
1000000 loops, best of 3: 1.11 µs per loop 

In [7]: %timeit [t - s for s, t in zip(a, a[1:])] 
1000000 loops, best of 3: 1.1 µs per loop 

Answer 2

使用recipe for pairwise从迭代工具文档：

from itertools import izip, tee 
def pairwise(iterable): 
    "s -> (s0,s1), (s1,s2), (s2, s3), ..." 
    a, b = tee(iterable) 
    next(b, None) 
    return izip(a, b) 

使用它是这样的：

>>> a = [0, 4, 10, 100] 
>>> [y-x for x,y in pairwise(a)] 
[4, 6, 90] 

Answer 3

[x - a[i-1] if i else None for i, x in enumerate(a)][1:]