python去除列表中重复元素的方法

列表中元素位置的索引用的是L.index

本文实例讲述了Python去除列表中重复元素的方法。分享给大家供大家参考。具体如下：

比较容易记忆的是用内置的set

l1 = ["b","c","d","b","c","a","a"] 
l2 = list(set(l1)) 
print (l2)

还有一种据说速度更快的，没测试过两者的速度差别

l1 = ["b","c","d","b","c","a","a"] 
l2 = {}.fromkeys(l1).keys() 
print (l2)

这两种都有个缺点，祛除重复元素后排序变了：

["a", "c", "b", "d"]

如果想要保持他们原来的排序：

用list类的sort方法

l1 = ["b","c","d","b","c","a","a"] 
l2 = list(set(l1)) 
l2.sort(key=l1.index) 
print (l2)

也可以这样写

#Python学习交流群：711312441
l1 = ["b","c","d","b","c","a","a"] 
l2 = sorted(set(l1),key=l1.index) 
print (l2)

也可以用遍历

l1 = ["b","c","d","b","c","a","a"] 
l2 = [] 
for i in l1: 
  if not i in l2: 
    l2.append(i) 
print (l2)

上面的代码也可以这样写

l1 = ["b","c","d","b","c","a","a"] 
l2 = [] 
[l2.append(i) for i in l1 if not i in l2] 
print (l2)

这样就可以保证排序不变了

在pythoncook里边提到的一种面向可哈希数据的取出相同元素的方法是：利用到了集合与生成器set、yield

def dedupe(items):
seen = set()
for item in items:
if item not in seen:
yield item
seen.add(item) 

不可变类型可哈希，可变类型不可哈希，对于不可哈希的数据
上述代码改成：

def dedupe(items, key=None):
seen = set()
for item in items:
val = item if key is None else key(item)
if val not in seen:
yield item
seen.add(val)