How to subtract backwards in a list in Python 3?

Question

I am trying to subtract a list backwards in Python. This is the code:

list_1 = [1,2,5,7,9,85]

The subtraction should go like this: index 1 - index 0, index 2 - index 1, and so on and so forth. This is the output:

1
3
2
2
76

How can i do something like this using Python 3?

Answer 1

Using map and operator and itertools.islice , this way you are avoiding intermediate lists creation or memory overhead and also avoids using python native for loop:

import operator
from itertools import islice
list_1 = [1,2,5,7,9,85]

result = list(map(operator.sub, islice(list_1, 1, None),list_1))

Here you have a live example

Answer 2

使用zip ：

[i - j for i, j in zip(list_1[1:], list_1)]

Answer 3

You can use a good old-fashioned for loop:

for i in range(1, len(list_1)):
    print list_1[i]-list_1[i-1]

Answer 4

Try this:

list_1 = [1,2,5,7,9,85]
for i in range(len(list_1)-1,1,-1):
    list_1[i] = list_1[i]-list_1[i-1]
print(list_1)

Note: iterate backwards to get expected answer.

Answer 5

One-liner using list comprehension.

Iterate from zero to the penultimate index and do the subtraction.

[ (list_1[i+1] - list_1[i]) for i in range(len(list_1)-1)]

Answer 6

    print [a[i+1]- a[i] for i in range(len(a)-1)]

这种单行返回一个列表，其元素是list_1中连续数字的差。