乘相鄰的元素，並將它們添加

Question

我要先後乘列表的相鄰元素，並添加乘法：

• ([1,2,3,4])應該執行(1*2+2*3+3*4)和
• [1,2,3]我想8因爲(1*2)+(2*3)

Answer 1

功能使用summaplambda和zip

def my_math(lst): 
    return sum(map(lambda x: x[0]*x[1], zip(lst, lst[1:]))) 

>>> my_math([1,2,3]) 
8 
>>> my_math([1,2,3,4]) 
20 
>>> my_math([1,2,3,4,5]) 
40 

Answer 2

使用列表理解：

>>> mylist = [1,2,3,4] 
>>> sum(mylist[i] * mylist[i + 1] for i in range(len(mylist) - 1)) 
20 

Answer 3

試試這個：

x=[1,2,3,4] 
print sum(a*b for a,b in zip(x, x[1:])) 
#prints 20 

Answer 4

使用pairwise itertools recipe：

>>> sum(a * b for (a, b) in pairwise([1, 2, 3, 4])) 
20 
>>> sum(a * b for (a, b) in pairwise([1, 2, 3])) 
8 

我需要什麼CHAN ge想要function([1,2,3,4])執行(1*2*3*4)？

>>> from functools import reduce 
>>> from operator import mul 
>>> reduce(mul, [1, 2, 3, 4]) 
24 

Answer 5

In [88]: mylist = [1,2,3,4] 

In [89]: sum(itertools.imap(lambda t: operator.mul(*t), itertools.izip(mylist, itertools.islice(mylist, 1, len(mylist))))) 
Out[89]: 20 

Answer 6

沒有任何名單切片生成表達式/份

>>> mylist = [1,2,3,4] 
>>> sum(mylist[i-1] * j for i, j in enumerate(mylist) if i) 
20