如何從字符串單數，同時保留順序

Question

def pos_and_neg(a): 
    seen = set() 
    seen_add = seen.add 
    return [ x for x in a if not (x in seen or seen_add(x))] 

print pos_and_neg([1,2,3,-1,-3]) 

這需要返回

[1,3,-1,-3] 

Answer 1

def pos_and_neg(a): 
    return [ x for x in a if (x*(-1)) in a] 
print pos_and_neg([1, 4, 6, -1, -4, -6, 5, 7, -7]) 

輸出： - [1, 4, 6, -1, -4, -6, 7, -7]

Answer 2

你可以做這樣的事情

def pos_and_neg(l): 
    unique = set(l) # use a set for faster lookups 
    return [i for i in l if (i*-1) in unique] 

>>> pos_and_neg([1,4,5,6,-1,2,-4,-6]) 
[1, 4, 6, -1, -4, -6] 

雖然它不會噸處理重複，所以如果你有[1,1,-1]所有的價值將被保留，而不是刪除1之一。