為什么? lists:usort/2 不可以 unique sort ?

patagonia2

1. %-module(x).
   
2. -define(P, io:format).
   
3. 
   
4. main(_) ->
   
5.     L = [3, 3, 2, 1, 1, 4],
   
6.     X = lists:usort( fun(A, B) -> A < B end, L ),
   
7.     Y = lists:usort( fun(A, B) -> A > B end, L ),
   
8.     ?P ("X = ~p~n", [X]),
   
9.     ?P ("Y = ~p~n", [Y])
   
10. .
    

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為什么? lists:usort/2 不可以 unique sort ?

1. X = [1,1,2,3,3,4]
   
2. Y = [4,3,3,2,1,1]
   

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為什么輸出不是

1. X = [1,2,3,4]
   
2. Y = [4,3,2,1]
   

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shijiang1130

1. 6> L = [3, 3, 2, 1, 1, 4].
   
2. [3,3,2,1,1,4]
   
3. 7> lists:usort(L).
   
4. [1,2,3,4]
   

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代碼哥

patagonia2

正解: STDLIB User's Guide 正
Fun(A, B) should return true if A compares less than or equal to B in the ordering, false otherwise.

1.     X = lists:usort( fun(A, B) -> A =< B end, L ),
   
2.     Y = lists:usort( fun(A, B) -> A >= B end, L ),

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shijiang1130

patagonia2

回復 4# shijiang1130


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