> For the complete documentation index, see [llms.txt](https://eastlakeside.gitbook.io/interpy-zh/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eastlakeside.gitbook.io/interpy-zh/set_data_structure.md).

# set 数据结构

`set`（集合）是一个非常有用的数据结构。它与列表（`list`）的行为类似，区别在于 `set` 不能包含重复的值。\
这在很多情况下非常有用。例如你可能想检查列表中是否包含重复的元素，你有两个选择，第一个需要使用 `for` 循环，就像这样：

```python
some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']

duplicates = []
for value in some_list:
    if some_list.count(value) > 1:
        if value not in duplicates:
            duplicates.append(value)

print(duplicates)
### 输出: ['b', 'n']
```

但还有一种更简单更优雅的解决方案，那就是使用`集合（sets）`，你直接这样做：

```python
some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']
duplicates = set([x for x in some_list if some_list.count(x) > 1])
print(duplicates)
### 输出: set(['b', 'n'])
```

集合还有一些其它方法，下面我们介绍其中一部分。

## 交集（intersection）

你可以对比两个集合的交集（两个集合中都有的数据），如下：

```python
valid = set(['yellow', 'red', 'blue', 'green', 'black'])
input_set = set(['red', 'brown'])
print(input_set.intersection(valid))
### 输出: set(['red'])
```

## 差集（difference）

你可以用差集找出无效的数据，相当于用一个集合减去另一个集合的数据，例如：

```python
valid = set(['yellow', 'red', 'blue', 'green', 'black'])
input_set = set(['red', 'brown'])
print(input_set.difference(valid))
### 输出: set(['brown'])
```

你也可以用`{}`符号来创建集合，如：

```python
a_set = {'red', 'blue', 'green'}
print(type(a_set))
### 输出: <type 'set'>
```

集合还有一些其它方法，我会建议访问官方文档并做个快速阅读。


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