set 集合

Set

1、简介

• set中的元素：可hash(int, str, tuple, bool)，不重复，底层存储无序
• set集合中的元素必须是可hash，但set自己是不可hash，是可变的数据类型

2、应用(重点)

    利用set中元素不可重复，可给list去重

lst = [11, 11, 22, 22, 33, 33, 44, 44, 55, 55]

lst = list(set(lst))
print(lst)  # [33, 11, 44, 22, 55]  结果无序，但已去重

3、增删改查

1）增

• add

    重复的内容不会被添加到set集合中，新增对象须为可hash数据类型

s = {11, 22, 33, 44}

s.add("hello")
print(add)  # {33, 11, 44, 'hello', 22}

s.add(11)
print(s)  # {33, 11, 44, 'hello', 22}

• update

    迭代更新，新增对象可为可hash或不可hash数据类型

s = {11, 22, 33, 44}

s.update("hello")
print(s)  # {33, 'l', 11, 44, 'e', 22, 'o', 'h'}

s = {11, 22, 33, 44}

s.update([55, 66, 77])
print(s)  # {33, 66, 11, 44, 77, 22, 55}

2）删

• pop

    随机弹出一个

s = {11, 22, 33, 44}

num = s.pop()
print(s) # {11, 44, 22}
print(num) # 33

• remove

    根据元素内容进行删除，若元素不存在，则报错

s = {11, 22, 33, 44}

s.remove(11)
print(s)  # {33, 44, 22}

• clear

    清空set集合，若是set集合是空的，打印出来是set()，须与dict区分

s = {11, 22, 33, 44}

s.clear()
print(s)  # set()

3) 改

• set集合中数据没有索引，也无法定位一个元素，因此没有办法进行直接修改
• 可采用先删除后添加方式完成修改

s = {11, 22, 33, 44}

s.remove(11)
s.add(55)
print(s)  # {33, 44, 22, 55}

4）查

    set是一个可迭代对象，可进行for循环

for el in s:
    print(el)

4、经常使用操做

1）交集

• &

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1 & s2)  # {33, 44}

• intersection

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1.intersection(s2)) # {33, 44}

2)并集

• |

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1 | s2)  # {33, 22, 55, 11, 44}

• union

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1.union(s2))  # {33, 22, 55, 11, 44}

3)差集

    s1 - s2：获得s1中单独存在的

• -

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1 - s2)  # {11, 22}

• difference

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1.difference(s2))  # {11, 22}

4)反交集

    s1 ^ s2：获得一个新的集合，里面元素为两集合（s1, s2）不相同的元素

• ^

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1 ^ s2)  # {22, 55, 11}

• symmetric_difference

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1.symmetric_difference(s2))  # {22, 55, 11}

5)子集

    s1 < s2:判断s1是否为s2子集，返回True or False

• <

s1 = {11, 22, 33, 44}
s2 = {33, 44, 55}

print(s1 < s2)  # False

• issubset

s1 = {11, 22, 33, 44}
s2 = {11, 22, 33, 44, 55}

print(s1.issubset(s2)) # True

6)超集

    s1 > s2：判断s1是否为s2的超集，也即s2是否为s1的子集，返回True or False

• >

s1 = {11, 22, 33, 44}
s2 = {11, 22, 33}

print(s1 > s2)  # True

• issuperset

s1 = {11, 22, 33, 44}
s2 = {11, 22, 33}

print(s1.issuperset(s2))  # True

7) frozenset

• frozenset是一种不可变，可hash的集合
• 经过frozenset可将可变的数据类型转换成不可变，可hash的frozenset集合

s = [44, 55, 66]

s1 = {11, 22, 33, s}  # 报错  TypeError: unhashable type: 'list'

s = frozenset([44, 55, 66])
print(s)  # frozenset({66, 44, 55})

s1 = {11, 22, 33, s}  # 正常
 

s = frozenset([1,2,3,4,5])
print(s)  # frozenset({1, 2, 3, 4, 5})
for el in s:
    print(el)  # 1 2 3 4 5