通過使用第一個數組項目對條目進行索引來合併兩個數組？

Question

假設我有

a = [1,2,1,3,2,2] 
b = [4,7,9,5,6,11] 

我期待

c = [[4,9],[7,6,11],[5]] 

因爲你可能會看到生成的子列表是在由列表a指出的指數。我們將如何在Python中做什麼？

Answer 1

IIUC，我只是在條件循環：

def combine(a,b): 
    c = [[] for _ in range(max(a))] 
    for i, elem in zip(a, b): 
     c[i-1].append(elem) 
    return c 

這給

>>> a = [1, 1, 1, 2, 2, 3] 
>>> b = [4, 7, 9, 5, 6, 11] 
>>> combine(a,b) 
[[4, 7, 9], [5, 6], [11]] 
>>> a = [1,2,1,3,2,2] 
>>> b = [4,7,9,5,6,11] 
>>> combine(a,b) 
[[4, 9], [7, 6, 11], [5]] 

Answer 2

你可以使用一個defaultdict：

>>> from collections import defaultdict 
>>> d = defaultdict(list) 
>>> a = [1,1,1,2,2,3] 
>>> b = [4,7,9,5,6,11] 
>>> for k,v in zip(a,b): 
...  d[k].append(v) 
... 
>>>[x[1] for x in sorted(d.items())] 
[[4, 7, 9], [5, 6], [11]]