Question

给出此列表：

a = ['a','b','b','b','c','c','d','e','e']

我想返回一个列表列表，每个列表包含如下值的开始和结束索引：

[[0,0], [1,3], [4,5], [6,6], [7,8]]

Answer 1

使用itertools.groupby（doc）：

a = ['a','b','b','b','c','c','d','e','e']

from itertools import groupby

last_index = 0
out = []
for v, g in groupby(enumerate(a), lambda k: k[1]):
    l = [*g]
    out.append([last_index, l[-1][0]])
    last_index += len(l)

print(out)

打印：

[[0, 0], [1, 3], [4, 5], [6, 6], [7, 8]]

Answer 2

如果列表已排序

if len(a) == 0:
  return []
result = []
firstSeenIndex, elementInWatch = 0,a[0]
for i,ele in enumerate(1,a[1:]):
    if ele == elementInWatch:
       continue
    else:
       result.append([firstSeenIndex,i-1])
       firstSeenIndex = i
       elementInWatch= ele
result.append([firstSeenIndex,len(a)-1]
return result

注意：有很多更好的方法可以做到，我希望这是直观的。

Answer 3

同时使用itertools.groupby和itertools.accumulate，我们可以避免自己积累索引。

此外，这不会为原始数组中的每个元素添加额外的数据，而只会为每个组添加额外的数据。

尝试一下：

from itertools import groupby, accumulate

a = ['a', 'b', 'b', 'b', 'c', 'c', 'd', 'e', 'e']

lens = [len(list(g)) for _, g in groupby(a)]
result = [[accumulated_length-current_length, accumulated_length-1] for current_length, accumulated_length in zip(lens, accumulate(lens))]

print(result)

输出：

[[0, 0], [1, 3], [4, 5], [6, 6], [7, 8]]

Answer 4

def start_stop_indice(a):
    result = []   # init empty list
    start_inx,end_inx,count = 0,0,0 # init indexs and counts to 0

    # while the starting index plus the count of records <= the length of the list
    while start_inx + count <= len(a): 
        # count is the number of times a record is in the list
        count = a.count(a[start_inx])  

        # end_index is the starting index + number of occurances - 1
        end_inx = start_inx + count - 1 

        # append a list of starting and ending indexs to the results list
        result.append([start_inx,end_inx]) 

        # add the count to the starting index to get next value
        start_inx += count

    return result

if __name__ == '__main__':
    a = ['a','b','b','b','c','c','d','e','e']
    print(start_stop_indice(a))

Python返回值的开始/停止值

4 个答案: