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71 lines
1.9 KiB
Markdown
71 lines
1.9 KiB
Markdown
# Set
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[](https://gezf7g7pd5.execute-api.ap-northeast-1.amazonaws.com/default/source_up_to_date?owner=erg-lang&repos=erg&ref=main&path=doc/EN/syntax/15_set.md&commit_hash=e959b3e54bfa8cee4929743b0193a129e7525c61)
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一個Set代表一個集合，它在結構上是一個重復的無序數組
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```python
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assert Set.from([1, 2, 3, 2, 1]) == {1, 2, 3}
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assert {1, 2} == {1, 1, 2} # 重復的被自動刪除
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assert {1, 2} == {2, 1}
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```
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它也可以用類型和長度來聲明
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```python
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a: {Int; 3} = {0, 1, 2} # OK
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b: {Int; 3} = {0, 0, 0} # NG，重復的內容被刪除，長度也會改變
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# TypeError: the type of b is mismatched
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# expected: Set(Int, 3)
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# but found: Set({0, }, 1)
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```
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此外，只有實現`Eq`跟蹤的對象才能成為集合的元素
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因此，不可能使用Floats等作為集合元素
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```python,compile_fail
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d = {0.0, 1.0} # NG
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#
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# 1│ d = {0.0, 1.0}
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# ^^^^^^^^
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# TypeError: the type of _ is mismatched:
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# expected: Eq(Float)
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# but found: {0.0, 1.0, }
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```
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Set可以執行集合操作
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```python
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assert 1 in {1, 2, 3}
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assert not 1 in {}
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assert {1} or {2} == {1, 2}
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assert {1, 2} and {2, 3} == {2}
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assert {1, 2} not {2} == {1}
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```
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Set是同質集合。為了使不同類的對象共存，它們必須同質化
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```python
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s: {Int or Str} = {"a", 1, "b", -1}
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```
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## Sets為類型
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Sets也可以被視為類型。這種類型稱為 _枚舉類型_
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```python
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i: {1, 2, 3} = 1
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assert i in {1, 2, 3}
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```
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Set的元素直接是類型的元素
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請注意，這些Set本身是不同的
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```python
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mut_set = {1, 2, 3}.into {Int; !3}
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mut_set.insert!(4)
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```
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<p align='center'>
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</p>
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