集合和数据结构

集合和数据结构

迭代

序列迭代由 iterate 实现广义的 for 循环

for i in iter   # or  "for i = iter"
    # body
end

被转换成

next = iterate(iter)
while next !== nothing
    (i, state) = next
    # body
    next = iterate(iter, state)
end

state 对象可以是任何对象，并且对于每个可迭代类型应该选择合适的 state 对象。请参照帮助文档接口的迭代小节来获取关于定义一个常见迭代类型的更多细节。

Base.iterate — Function

iterate(iter [, state]) -> Union{Nothing, Tuple{Any, Any}}

Advance the iterator to obtain the next element. If no elements remain, nothing should be returned. Otherwise, a 2-tuple of the next element and the new iteration state should be returned.

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Base.IteratorSize — Type

IteratorSize(itertype::Type) -> IteratorSize

Given the type of an iterator, return one of the following values:

SizeUnknown() if the length (number of elements) cannot be determined in advance.
HasLength() if there is a fixed, finite length.
HasShape{N}() if there is a known length plus a notion of multidimensional shape (as for an array). In this case N should give the number of dimensions, and the axes function is valid for the iterator.
IsInfinite() if the iterator yields values forever.

The default value (for iterators that do not define this function) is HasLength(). This means that most iterators are assumed to implement length.

This trait is generally used to select between algorithms that pre-allocate space for their result, and algorithms that resize their result incrementally.

julia> Base.IteratorSize(1:5)
Base.HasShape{1}()
julia> Base.IteratorSize((2,3))
Base.HasLength()

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Base.IteratorEltype — Type

IteratorEltype(itertype::Type) -> IteratorEltype

Given the type of an iterator, return one of the following values:

EltypeUnknown() if the type of elements yielded by the iterator is not known in advance.
HasEltype() if the element type is known, and eltype would return a meaningful value.

HasEltype() is the default, since iterators are assumed to implement eltype.

This trait is generally used to select between algorithms that pre-allocate a specific type of result, and algorithms that pick a result type based on the types of yielded values.

julia> Base.IteratorEltype(1:5)
Base.HasEltype()

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以下类型均完全实现了上述函数：

AbstractRange
UnitRange
Tuple
Number
AbstractArray
BitSet
IdDict
Dict
WeakKeyDict
EachLine
AbstractString
Set
Pair
NamedTuple

构造函数和类型

Base.AbstractRange — Type

AbstractRange{T}

Supertype for ranges with elements of type T. UnitRange and other types are subtypes of this.

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Base.OrdinalRange — Type

OrdinalRange{T, S} <: AbstractRange{T}

Supertype for ordinal ranges with elements of type T with spacing(s) of type S. The steps should be always-exact multiples of oneunit, and T should be a “discrete” type, which cannot have values smaller than oneunit. For example, Integer or Date types would qualify, whereas Float64 would not (since this type can represent values smaller than oneunit(Float64). UnitRange, StepRange, and other types are subtypes of this.

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Base.AbstractUnitRange — Type

AbstractUnitRange{T} <: OrdinalRange{T, T}

Supertype for ranges with a step size of oneunit(T) with elements of type T. UnitRange and other types are subtypes of this.

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Base.StepRange — Type

StepRange{T, S} <: OrdinalRange{T, S}

Ranges with elements of type T with spacing of type S. The step between each element is constant, and the range is defined in terms of a start and stop of type T and a step of type S. Neither T nor S should be floating point types. The syntax a:b:c with b > 1 and a, b, and c all integers creates a StepRange.

Examples

julia> collect(StepRange(1, Int8(2), 10))
5-element Vector{Int64}:
 1
 3
 5
 7
 9
julia> typeof(StepRange(1, Int8(2), 10))
StepRange{Int64, Int8}
julia> typeof(1:3:6)
StepRange{Int64, Int64}

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Base.UnitRange — Type

UnitRange{T<:Real}

A range parameterized by a start and stop of type T, filled with elements spaced by 1 from start until stop is exceeded. The syntax a:b with a and b both Integers creates a UnitRange.

Examples

julia> collect(UnitRange(2.3, 5.2))
3-element Vector{Float64}:
 2.3
 3.3
 4.3
julia> typeof(1:10)
UnitRange{Int64}

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Base.LinRange — Type

LinRange{T,L}

A range with len linearly spaced elements between its start and stop. The size of the spacing is controlled by len, which must be an Integer.

Examples

julia> LinRange(1.5, 5.5, 9)
9-element LinRange{Float64, Int64}:
 1.5,2.0,2.5,3.0,3.5,4.0,4.5,5.0,5.5

Compared to using range, directly constructing a LinRange should have less overhead but won’t try to correct for floating point errors:

julia> collect(range(-0.1, 0.3, length=5))
5-element Array{Float64,1}:
 -0.1
  0.0
  0.1
  0.2
  0.3
julia> collect(LinRange(-0.1, 0.3, 5))
5-element Array{Float64,1}:
 -0.1
 -1.3877787807814457e-17
  0.09999999999999999
  0.19999999999999998
  0.3

source

通用集合

Base.isempty — Function

isempty(collection) -> Bool

Determine whether a collection is empty (has no elements).

Examples

julia> isempty([])
true
julia> isempty([1 2 3])
false

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isempty(condition)

Return true if no tasks are waiting on the condition, false otherwise.

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Base.empty! — Function

empty!(collection) -> collection

Remove all elements from a collection.

Examples

julia> A = Dict("a" => 1, "b" => 2)
Dict{String, Int64} with 2 entries:
  "b" => 2
  "a" => 1
julia> empty!(A);
julia> A
Dict{String, Int64}()

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Base.length — Function

length(collection) -> Integer

Return the number of elements in the collection.

Use lastindex to get the last valid index of an indexable collection.

可迭代集合

Base.in — Function

in(item, collection) -> Bool
∈(item, collection) -> Bool

Determine whether an item is in the given collection, in the sense that it is \== to one of the values generated by iterating over the collection. Returns a Bool value, except if item is missing or collection contains missing but not item, in which case missing is returned (three-valued logic, matching the behavior of any and \==).

Some collections follow a slightly different definition. For example, Sets check whether the item isequal to one of the elements. Dicts look for key=>value pairs, and the key is compared using isequal. To test for the presence of a key in a dictionary, use haskey or k in keys(dict). For these collections, the result is always a Bool and never missing.

To determine whether an item is not in a given collection, see :∉. You may also negate the in by doing !(a in b) which is logically similar to “not in”.

When broadcasting with in.(items, collection) or items .∈ collection, both item and collection are broadcasted over, which is often not what is intended. For example, if both arguments are vectors (and the dimensions match), the result is a vector indicating whether each value in collection items is in the value at the corresponding position in collection. To get a vector indicating whether each value in items is in collection, wrap collection in a tuple or a Ref like this: in.(items, Ref(collection)) or items .∈ Ref(collection).

Examples

julia> a = 1:3:20
1:3:19
julia> 4 in a
true
julia> 5 in a
false
julia> missing in [1, 2]
missing
julia> 1 in [2, missing]
missing
julia> 1 in [1, missing]
true
julia> missing in Set([1, 2])
false
julia> !(21 in a)
true
julia> !(19 in a)
false
julia> [1, 2] .∈ [2, 3]
2-element BitVector:
 0
 0
julia> [1, 2] .∈ ([2, 3],)
2-element BitVector:
 0
 1

See also: insorted, contains, occursin, issubset.

source

Base.:∉ — Function

∉(item, collection) -> Bool
∌(collection, item) -> Bool

Negation of ∈ and ∋, i.e. checks that item is not in collection.

When broadcasting with items .∉ collection, both item and collection are broadcasted over, which is often not what is intended. For example, if both arguments are vectors (and the dimensions match), the result is a vector indicating whether each value in collection items is not in the value at the corresponding position in collection. To get a vector indicating whether each value in items is not in collection, wrap collection in a tuple or a Ref like this: items .∉ Ref(collection).

Examples

julia> 1 ∉ 2:4
true
julia> 1 ∉ 1:3
false
julia> [1, 2] .∉ [2, 3]
2-element BitVector:
 1
 1
julia> [1, 2] .∉ ([2, 3],)
2-element BitVector:
 1
 0

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Base.eltype — Function

eltype(type)

Determine the type of the elements generated by iterating a collection of the given type. For dictionary types, this will be a Pair{KeyType,ValType}. The definition eltype(x) = eltype(typeof(x)) is provided for convenience so that instances can be passed instead of types. However the form that accepts a type argument should be defined for new types.

可索引集合

Base.getindex — Function

getindex(collection, key...)

Retrieve the value(s) stored at the given key or index within a collection. The syntax a[i,j,...] is converted by the compiler to getindex(a, i, j, ...).

字典

Dict 是一个标准字典。其实现利用了 hash 作为键的哈希函数和 isequal 来决定是否相等。对于自定义类型，可以定义这两个函数来重载它们在哈希表内的存储方式。

IdDict 是一种特殊的哈希表，在里面键始终是对象标识符。

WeakKeyDict 是一个哈希表的实现，里面键是对象的弱引用，所以即使键在哈希表中被引用也有可能被垃圾回收。它像 Dict 一样使用 hash 来做哈希和 isequal 来做相等判断，但是它不会在插入时转换键，这点不像 Dict。

Dicts 可以由传递含有 => 的成对对象给 Dict 的构造函数来被创建：Dict("A"=>1, "B"=>2)。这个调用会尝试从键值对中推到类型信息（比如这个例子创造了一个 Dict{String, Int64}）。为了显式指定类型，请使用语法 Dict{KeyType,ValueType}(...)。例如：Dict{String,Int32}("A"=>1, "B"=>2)。

字典也可以用生成器创建。例如：Dict(i => f(i) for i = 1:10)。

对于字典 D，若键 x 的值存在，则语法 D[x] 返回 x 的值；否则抛出一个错误。 D[x] = y 存储键值对 x => y 到 D 中，会覆盖键 x 的已有的值。多个参数传入D[...] 会被转化成元组；例如：语法 D[x,y] 等于 D[(x,y)]，也就是说，它指向键为元组 (x,y) 的值。

Base.AbstractDict — Type

AbstractDict{K, V}

Supertype for dictionary-like types with keys of type K and values of type V. Dict, IdDict and other types are subtypes of this. An AbstractDict{K, V} should be an iterator of Pair{K, V}.

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Base.Dict — Type

Dict([itr])

Dict{K,V}() constructs a hash table with keys of type K and values of type V. Keys are compared with isequal and hashed with hash.

Given a single iterable argument, constructs a Dict whose key-value pairs are taken from 2-tuples (key,value) generated by the argument.

Examples

julia> Dict([("A", 1), ("B", 2)])
Dict{String, Int64} with 2 entries:
  "B" => 2
  "A" => 1

Alternatively, a sequence of pair arguments may be passed.

julia> Dict("A"=>1, "B"=>2)
Dict{String, Int64} with 2 entries:
  "B" => 2
  "A" => 1

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Base.IdDict — Type

IdDict([itr])

IdDict{K,V}() constructs a hash table using objectid as hash and === as equality with keys of type K and values of type V.

See Dict for further help. In the example below, The Dict keys are all isequal and therefore get hashed the same, so they get overwritten. The IdDict hashes by object-id, and thus preserves the 3 different keys.

Examples

julia> Dict(true => "yes", 1 => "no", 1.0 => "maybe")
Dict{Real, String} with 1 entry:
  1.0 => "maybe"
julia> IdDict(true => "yes", 1 => "no", 1.0 => "maybe")
IdDict{Any, String} with 3 entries:
  true => "yes"
  1.0  => "maybe"
  1    => "no"

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Base.WeakKeyDict — Type

WeakKeyDict([itr])

WeakKeyDict() constructs a hash table where the keys are weak references to objects which may be garbage collected even when referenced in a hash table.

See Dict for further help. Note, unlike Dict, WeakKeyDict does not convert keys on insertion, as this would imply the key object was unreferenced anywhere before insertion.

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Base.ImmutableDict — Type

ImmutableDict

ImmutableDict is a dictionary implemented as an immutable linked list, which is optimal for small dictionaries that are constructed over many individual insertions. Note that it is not possible to remove a value, although it can be partially overridden and hidden by inserting a new value with the same key.

ImmutableDict(KV::Pair)

Create a new entry in the ImmutableDict for a key => value pair

use (key => value) in dict to see if this particular combination is in the properties set
use get(dict, key, default) to retrieve the most recent value for a particular key

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Base.haskey — Function

haskey(collection, key) -> Bool

Determine whether a collection has a mapping for a given key.

Examples

julia> D = Dict('a'=>2, 'b'=>3)
Dict{Char, Int64} with 2 entries:
  'a' => 2
  'b' => 3
julia> haskey(D, 'a')
true
julia> haskey(D, 'c')
false

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Base.get — Function

get(collection, key, default)

Return the value stored for the given key, or the given default value if no mapping for the key is present.

Julia 1.7

For tuples and numbers, this function requires at least Julia 1.7.

Examples

julia> d = Dict("a"=>1, "b"=>2);
julia> get(d, "a", 3)
1
julia> get(d, "c", 3)
3

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get(f::Function, collection, key)

Return the value stored for the given key, or if no mapping for the key is present, return f(). Use get! to also store the default value in the dictionary.

This is intended to be called using do block syntax

get(dict, key) do
    # default value calculated here
    time()
end

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Base.get! — Function

get!(collection, key, default)

Return the value stored for the given key, or if no mapping for the key is present, store key => default, and return default.

Examples

julia> d = Dict("a"=>1, "b"=>2, "c"=>3);
julia> get!(d, "a", 5)
1
julia> get!(d, "d", 4)
4
julia> d
Dict{String, Int64} with 4 entries:
  "c" => 3
  "b" => 2
  "a" => 1
  "d" => 4

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get!(f::Function, collection, key)

Return the value stored for the given key, or if no mapping for the key is present, store key => f(), and return f().

This is intended to be called using do block syntax.

Examples

julia> squares = Dict{Int, Int}();
julia> function get_square!(d, i)
           get!(d, i) do
               i^2
           end
       end
get_square! (generic function with 1 method)
julia> get_square!(squares, 2)
4
julia> squares
Dict{Int64, Int64} with 1 entry:
  2 => 4

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Base.getkey — Function

getkey(collection, key, default)

Return the key matching argument key if one exists in collection, otherwise return default.

Examples

julia> D = Dict('a'=>2, 'b'=>3)
Dict{Char, Int64} with 2 entries:
  'a' => 2
  'b' => 3
julia> getkey(D, 'a', 1)
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
julia> getkey(D, 'd', 'a')
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)

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Base.delete! — Function

delete!(collection, key)

Delete the mapping for the given key in a collection, if any, and return the collection.

Examples

julia> d = Dict("a"=>1, "b"=>2)
Dict{String, Int64} with 2 entries:
  "b" => 2
  "a" => 1
julia> delete!(d, "b")
Dict{String, Int64} with 1 entry:
  "a" => 1
julia> delete!(d, "b") # d is left unchanged
Dict{String, Int64} with 1 entry:
  "a" => 1

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Base.pop! — Method

pop!(collection, key[, default])

Delete and return the mapping for key if it exists in collection, otherwise return default, or throw an error if default is not specified.

Examples

julia> d = Dict("a"=>1, "b"=>2, "c"=>3);
julia> pop!(d, "a")
1
julia> pop!(d, "d")
ERROR: KeyError: key "d" not found
Stacktrace:
[...]
julia> pop!(d, "e", 4)
4

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Base.keys — Function

keys(iterator)

For an iterator or collection that has keys and values (e.g. arrays and dictionaries), return an iterator over the keys.

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Base.values — Function

values(iterator)

For an iterator or collection that has keys and values, return an iterator over the values. This function simply returns its argument by default, since the elements of a general iterator are normally considered its “values”.

Examples

julia> d = Dict("a"=>1, "b"=>2);
julia> values(d)
ValueIterator for a Dict{String, Int64} with 2 entries. Values:
  2
  1
julia> values([2])
1-element Vector{Int64}:
 2

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values(a::AbstractDict)

Return an iterator over all values in a collection. collect(values(a)) returns an array of values. When the values are stored internally in a hash table, as is the case for Dict, the order in which they are returned may vary. But keys(a) and values(a) both iterate a and return the elements in the same order.

Examples

julia> D = Dict('a'=>2, 'b'=>3)
Dict{Char, Int64} with 2 entries:
  'a' => 2
  'b' => 3
julia> collect(values(D))
2-element Vector{Int64}:
 2
 3

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Base.pairs — Function

pairs(IndexLinear(), A)
pairs(IndexCartesian(), A)
pairs(IndexStyle(A), A)

An iterator that accesses each element of the array A, returning i => x, where i is the index for the element and x = A[i]. Identical to pairs(A), except that the style of index can be selected. Also similar to enumerate(A), except i will be a valid index for A, while enumerate always counts from 1 regardless of the indices of A.

Specifying IndexLinear() ensures that i will be an integer; specifying IndexCartesian() ensures that i will be a CartesianIndex; specifying IndexStyle(A) chooses whichever has been defined as the native indexing style for array A.

Mutation of the bounds of the underlying array will invalidate this iterator.

Examples

julia> A = ["a" "d"; "b" "e"; "c" "f"];
julia> for (index, value) in pairs(IndexStyle(A), A)
           println("$index $value")
       end
1 a
2 b
3 c
4 d
5 e
6 f
julia> S = view(A, 1:2, :);
julia> for (index, value) in pairs(IndexStyle(S), S)
           println("$index $value")
       end
CartesianIndex(1, 1) a
CartesianIndex(2, 1) b
CartesianIndex(1, 2) d
CartesianIndex(2, 2) e

类似 Set 的集合

Base.AbstractSet — Type

AbstractSet{T}

Supertype for set-like types whose elements are of type T. Set, BitSet and other types are subtypes of this.

source

Base.Set — Type

Set([itr])

Construct a Set of the values generated by the given iterable object, or an empty set. Should be used instead of BitSet for sparse integer sets, or for sets of arbitrary objects.

双端队列

Base.push! — Function

push!(collection, items...) -> collection

Insert one or more items in collection. If collection is an ordered container, the items are inserted at the end (in the given order).

Examples

julia> push!([1, 2, 3], 4, 5, 6)
6-element Vector{Int64}:
 1
 2
 3
 4
 5
 6

If collection is ordered, use append! to add all the elements of another collection to it. The result of the preceding example is equivalent to append!([1, 2, 3], [4, 5, 6]). For AbstractSet objects, union! can be used instead.

See sizehint! for notes about the performance model.

集合相关的实用工具

Core.Pair — Type

Pair(x, y)
x => y

Construct a Pair object with type Pair{typeof(x), typeof(y)}. The elements are stored in the fields first and second. They can also be accessed via iteration (but a Pair is treated as a single “scalar” for broadcasting operations).