擴展列表的“pythonic”方式

Question

我有一個代表更改時間點的列表和另一個值：

indexes_list = [5, 6, 8, 9, 12, 15]
# [ 5  6  8  9 12 15]
values_list = [i * 10 for i in range(6)]
# [ 0 10 20 30 40 50]

我想創建“完整”列表，在上面的例子中是：

expanded_values = [0, 0, 0, 0, 0, 0, 10, 20, 20, 30, 40, 40, 40, 50, 50, 50]
# [ 0  0  0  0  0  0 10 20 20 30 40 40 40 50 50 50]

我寫了一些東西，但感覺不對，我想有一種更好、更pythonic的方法來做到這一點：

result = []
for i in range(len(values_list)):
    if i == 0:
        tmp = [values_list[i]] * (indexes_list[i] + 1)
    else:
        tmp = [values_list[i]] * (indexes_list[i] - indexes_list[i - 1])
    result += tmp
# result = [0, 0, 0, 0, 0, 0, 10, 20, 20, 30, 40, 40, 40, 50, 50, 50]

Answer 1

用：

indexes_array = [5, 6, 8, 9, 12, 15]
values_array = [i * 10 for i, _ in enumerate(range(6))]

diffs = indexes_array[:1] + [j - i for i, j in zip(indexes_array, indexes_array[1:])]
res = [v for i, v in zip(diffs, values_array) for _ in range(i)]
print(res)

輸出

[0, 0, 0, 0, 0, 10, 20, 20, 30, 40, 40, 40, 50, 50, 50]

作為替代方案，您可以使用帶有扭曲的成對配方：

from itertools import tee


def pairwise(iterable, prepend):
    a, b = tee(iterable)
    yield prepend, next(b, None)
    yield from zip(a, b)


indices = [5, 6, 8, 9, 12, 15]
values = [i * 10 for i, _ in enumerate(range(6))]

differences = [second - first for first, second in pairwise(indices, prepend=0)]
res = [v for i, v in zip(differences, values) for _ in range(i)]

print(res)

輸出

[0, 0, 0, 0, 0, 10, 20, 20, 30, 40, 40, 40, 50, 50, 50]

最后，如果您正在做數值工作，我建議您使用numpy ，如下所示：

import numpy as np

indices = [5, 6, 8, 9, 12, 15]
values = [i * 10 for i, _ in enumerate(range(6))]


differences = np.diff(indices, prepend=0)
res = np.repeat(values, differences).tolist()
print(res)

Answer 2

我認為使用適當的庫是 Pythonic 的，在這種情況下是pandas ：

import pandas as pd

indexes_array = [5, 6, 8, 9, 12, 15]
values_array = [i * 10 for i in range(6)]

series = pd.Series(values_array, indexes_array).reindex(
    range(indexes_array[-1] + 1), method='backfill')

series

0      0
1      0
2      0
3      0
4      0
5      0
6     10
7     20
8     20
9     30
10    40
11    40
12    40
13    50
14    50
15    50
dtype: int64

有關詳細信息，請參閱reindex 文檔。

Answer 3

嘗試這個：

indexes_array = [5, 6, 8, 9, 12, 15]
# [ 5  6  8  9 12 15]
values_array = [i * 10 for i, _ in enumerate(range(6))]
# [ 0 10 20 30 40 50]

result = []
last_ind = 0
zipped = zip(indexes_array, values_array)

for ind, val in zipped:
    count = ind - last_ind
    last_ind = ind
    for i in range(count):
        result.append(val)
print(result)

輸出：

[0, 0, 0, 0, 0, 10, 20, 20, 30, 40, 40, 40, 50, 50, 50]

Answer 4

嘗試這個：

indexes_array = [5, 6, 8, 9, 12, 15]
values_array = [i * 10 for i, _ in enumerate(range(6))]
output=[]
for x in range(len(indexes_array)):
  if x ==0:
    output.extend([values_array[x]]*indexes_array[x])
  else:
    output.extend([values_array[x]]*(indexes_array[x]-indexes_array[x-1]))

print(output)

輸出是：

[0, 0, 0, 0, 0, 10, 20, 20, 30, 40, 40, 40, 50, 50, 50]