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70 lines
1.6 KiB
Markdown
70 lines
1.6 KiB
Markdown
# Set
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A set represents a collection, which is structurally a duplicate, unordered array.
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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} # duplicates are automatically removed
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assert {1, 2} == {2, 1}
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```
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Sets can be declared by specifying type and length.
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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, Duplicates are deleted, and the length changes.
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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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In addition, only objects that implement the `Eq` trait can be elements of the Set.
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Therefore, it is not possible to use the Set elements such as a Float.
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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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Sets can perform set operations.
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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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A set is a homogeneous collection. In order for objects of different classes to coexist, they must be homogenized.
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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 as types
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Sets can also be treated as types. Such types are called __Enum types__.
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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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Elements of the set are directly elements of the type.
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Note that the sets themselves are different.
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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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<a href='./14_record.md'>Previous</a> | <a href='./16_type.md'>Next</a>
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</p>
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