Python从右到左对角线列表

Question

I would like a list to be stored into another list from right to left diagonally without importing anything if possible

eg. list = 
[[1, 4, 6]
[6, 3, 7]
[2, 7, 9]]

say I'd like to store [6, 3, 2] into another list, how would i go about doing it? I have tried many ways for hours and still cant find a solution

Answer 1

The following snipped

l =[[1, 4, 6],
    [6, 3, 7],
    [2, 7, 9]]
d = len(l)
a = []
for i in range(0,d):
    a.append(l[i][d-1-i])
print(a)

results in the output you expected:

[6, 3, 2]

Answer 2

When you want to create a list out from another list, list comprehension is a very good way to go.

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

This list comprehension loops through the lists taking the the furthes back integer and the second furthes back and so on.

Answer 3

With a list comprehension:

l =[[1, 4, 6],
    [6, 3, 7],
    [2, 7, 9]]

diagonal = [row[-i]  for i, row in enumerate(l, start=1)]

print(diagonal)

Output

[6, 3, 2]

Answer 4

You can use a list comprehension and use list indexing twice to select your row and column:

L = [[1, 4, 6],
     [6, 3, 7],
     [2, 7, 9]]

n = len(L)
res = [L[i][n-i-1] for i in range(n)]
# [6, 3, 2]

An alternative formulation is to use enumerate as per @OlivierMelançon's solution.

If you can use a 3rd party library, you can use NumPy to extract the diagonal of a flipped array:

import numpy as np

arr = np.array(L)

res = np.diag(np.fliplr(arr))
# array([6, 3, 2])

Answer 5

Using numpy and rotate (90)

import numpy as np
list = [[1, 4, 6],[6, 3, 7],[2, 7, 9]]
np.diag(np.rot90(array))

Output :

array([6, 3, 2])

or without using numpy:

list = [[1, 4, 6],[6, 3, 7],[2, 7, 9]]

res=[]
i=-1
for elm in list :
    res.append(elm[i])
    i-=1

print res
#[6, 3, 2]