python |获取二维列表的第一个元素

Question

我有以下列表:

j = [
    [(1, 100), (2, 80), (3, 40)],
    [(2, 80), (1, 30), (4, 50), (3, 60)],
    [(1, 40), (2, 70), (4, 30)]
]

我怎样才能像这样打印每个第一个元素:

[1, 2 ,3]
[2, 1, 4, 3]
[1, 2, 4]

我试过

for i in j:
print(i[0])

谢谢!

Answer 1

使用 zip 和列表理解:

[next(zip(*i)) for i in j]

---

[(1, 2, 3), (2, 1, 4, 3), (1, 2, 4)]

或者使用嵌套循环:

[[v[0] for v in i] for i in j]

---

[[1, 2, 3], [2, 1, 4, 3], [1, 2, 4]]