使用 itertools.groupby 返回最长的连续负数列表

Question

Given the series:

series = [2, 6, 9, -1, 1, -3, -3, -3, 1,-4]

How do you return the list [-3, -3, -3] using itertools.groupby ?

Trying:

from itertools import groupby
max((list(g) for k, g in groupby(series, key=lambda i: i < 0)), key=len)

returns:

[2, 6, 9]

Thanks in advance

Answer 1

You could do:

from itertools import groupby

series = [2, 6, 9, -1, 1, -3, -3, -3, 1, -4]
result = max((list(group) for key, group in groupby(series) if key < 0), key=len)

print(result)

Output

[-3, -3, -3]

The problem with your code is that you are using the wrong key in the groupby, key=lambda i: i < 0 , just filter the results if the key is positive.

Answer 2

Check you k value for True or False.

from itertools import groupby
series = [2, 6, 9, -1, 1, -3, -3, -3, 1,-4]
x = max([list(g) for k, g in groupby(series, key=lambda i: i < 0) if k == True ], key=len)
print(x)