如何选择元组列表中的增加元素？

Question

I have the following list of tuples:

a = [(1, 2), (2, 4), (3, 1), (4, 4), (5, 2), (6, 8), (7, -1)]

I would like to select the elements which second value in the tuple is increasing compared to the previous one. For example I would select (2, 4) because 4 is superior to 2 , in the same manner I would select (4, 4) and (6, 8) .

Can this be done in a more elegant way than a loop starting explicitly on the second element ?

To clarify, I want to select the tuples which second elements are superior to the second element of the prior tuple.

Answer 1

>>> [right for left, right in pairwise(a) if right[1] > left[1]]
[(2, 4), (4, 4), (6, 8)]

Where pairwise is an itertools recipe you can find here .

Answer 2

You can use a list comprehension to do this fairly easily:

a = [a[i] for i in range(1, len(a)) if a[i][1] > a[i-1][1]]

This uses range(1, len(a)) to start from the second element in the list, then compares the second value in each tuple with the second value from the preceding tuple to determine whether it should be in the new list.

Alternatively, you could use zip to generate pairs of neighbouring tuples:

a = [two for one, two in zip(a, a[1:]) if two[1] > one[1]]

Answer 3

您可以使用enumerate来派生索引，然后进行列表理解：

a = [t[1] for t in enumerate(a[1:]) if t[1][1] > a[t[0]-1][1]]

Answer 4

You can use list comprehension

[i for i in a if (i[0] < i[1])]

Returns

[(1, 2), (2, 4), (6, 8)]

Edit: I was incorrect in my understanding of the question. The above code will return all tuples in which the second element is greater than the first. This is not the answer to the question OP asked.