Arrays

构造函数与类型

Core.AbstractArray — Type.

AbstractArray{T,N}

Supertype for N-dimensional arrays (or array-like types) with elements of type T. Array and other types are subtypes of this. See the manual section on the @ref man-interface-array">AbstractArray interface.

source

Base.AbstractVector — Type.

AbstractVector{T}

Supertype for one-dimensional arrays (or array-like types) with elements of type T. Alias for AbstractArray{T,1}.

source

Base.AbstractMatrix — Type.

AbstractMatrix{T}

Supertype for two-dimensional arrays (or array-like types) with elements of type T. Alias for AbstractArray{T,2}.

source

Base.AbstractVecOrMat — Constant.

AbstractVecOrMat{T}

Union type of AbstractVector{T} and AbstractMatrix{T}.

source

Core.Array — Type.

Array{T,N} <: AbstractArray{T,N}

N-dimensional dense array with elements of type T.

source

Core.Array — Method.

Array{T}(undef, dims)
Array{T,N}(undef, dims)

Construct an uninitialized N-dimensional Array containing elements of type T. N can either be supplied explicitly, as in Array{T,N}(undef, dims), or be determined by the length or number of dims. dims may be a tuple or a series of integer arguments corresponding to the lengths in each dimension. If the rank N is supplied explicitly, then it must match the length or number of dims. See undef.

Examples

julia> A = Array{Float64,2}(undef, 2, 3) # N given explicitly
2×3 Array{Float64,2}:
 6.90198e-310  6.90198e-310  6.90198e-310
 6.90198e-310  6.90198e-310  0.0
julia> B = Array{Float64}(undef, 2) # N determined by the input
2-element Array{Float64,1}:
 1.87103e-320
 0.0

source

Core.Array — Method.

Array{T}(nothing, dims)
Array{T,N}(nothing, dims)

Construct an N-dimensional Array containing elements of type T, initialized with nothing entries. Element type T must be able to hold these values, i.e. Nothing <: T.

Examples

julia> Array{Union{Nothing, String}}(nothing, 2)
2-element Array{Union{Nothing, String},1}:
 nothing
 nothing
julia> Array{Union{Nothing, Int}}(nothing, 2, 3)
2×3 Array{Union{Nothing, Int64},2}:
 nothing  nothing  nothing
 nothing  nothing  nothing

source

Core.Array — Method.

Array{T}(missing, dims)
Array{T,N}(missing, dims)

Construct an N-dimensional Array containing elements of type T, initialized with missing entries. Element type T must be able to hold these values, i.e. Missing <: T.

Examples

julia> Array{Union{Missing, String}}(missing, 2)
2-element Array{Union{Missing, String},1}:
 missing
 missing
julia> Array{Union{Missing, Int}}(missing, 2, 3)
2×3 Array{Union{Missing, Int64},2}:
 missing  missing  missing
 missing  missing  missing

source

Core.UndefInitializer — Type.

UndefInitializer

Singleton type used in array initialization, indicating the array-constructor-caller would like an uninitialized array. See also undef, an alias for UndefInitializer().

Examples

julia> Array{Float64,1}(UndefInitializer(), 3)
3-element Array{Float64,1}:
 2.2752528595e-314
 2.202942107e-314
 2.275252907e-314

source

Core.undef — Constant.

undef

Alias for UndefInitializer(), which constructs an instance of the singleton type UndefInitializer, used in array initialization to indicate the array-constructor-caller would like an uninitialized array.

Examples

julia> Array{Float64,1}(undef, 3)
3-element Array{Float64,1}:
 2.2752528595e-314
 2.202942107e-314
 2.275252907e-314

source

Base.Vector — Type.

Vector{T} <: AbstractVector{T}

One-dimensional dense array with elements of type T, often used to represent a mathematical vector. Alias for Array{T,1}.

source

Base.Vector — Method.

Vector{T}(undef, n)

Construct an uninitialized Vector{T} of length n. See undef.

Examples

julia> Vector{Float64}(undef, 3)
3-element Array{Float64,1}:
 6.90966e-310
 6.90966e-310
 6.90966e-310

source

Base.Vector — Method.

Vector{T}(nothing, m)

Construct a Vector{T} of length m, initialized with nothing entries. Element type T must be able to hold these values, i.e. Nothing <: T.

Examples

julia> Vector{Union{Nothing, String}}(nothing, 2)
2-element Array{Union{Nothing, String},1}:
 nothing
 nothing

source

Base.Vector — Method.

Vector{T}(missing, m)

Construct a Vector{T} of length m, initialized with missing entries. Element type T must be able to hold these values, i.e. Missing <: T.

Examples

julia> Vector{Union{Missing, String}}(missing, 2)
2-element Array{Union{Missing, String},1}:
 missing
 missing

source

Base.Matrix — Type.

Matrix{T} <: AbstractMatrix{T}

Two-dimensional dense array with elements of type T, often used to represent a mathematical matrix. Alias for Array{T,2}.

source

Base.Matrix — Method.

Matrix{T}(undef, m, n)

Construct an uninitialized Matrix{T} of size m×n. See undef.

Examples

julia> Matrix{Float64}(undef, 2, 3)
2×3 Array{Float64,2}:
 6.93517e-310  6.93517e-310  6.93517e-310
 6.93517e-310  6.93517e-310  1.29396e-320

source

Base.Matrix — Method.

Matrix{T}(nothing, m, n)

Construct a Matrix{T} of size m×n, initialized with nothing entries. Element type T must be able to hold these values, i.e. Nothing <: T.

Examples

julia> Matrix{Union{Nothing, String}}(nothing, 2, 3)
2×3 Array{Union{Nothing, String},2}:
 nothing  nothing  nothing
 nothing  nothing  nothing

source

Base.Matrix — Method.

Matrix{T}(missing, m, n)

Construct a Matrix{T} of size m×n, initialized with missing entries. Element type T must be able to hold these values, i.e. Missing <: T.

Examples

julia> Matrix{Union{Missing, String}}(missing, 2, 3)
2×3 Array{Union{Missing, String},2}:
 missing  missing  missing
 missing  missing  missing

source

Base.VecOrMat — Constant.

VecOrMat{T}

Union type of Vector{T} and Matrix{T}.

source

Core.DenseArray — Type.

DenseArray{T, N} <: AbstractArray{T,N}

N-dimensional dense array with elements of type T. The elements of a dense array are stored contiguously in memory.

source

Base.DenseVector — Type.

DenseVector{T}

One-dimensional DenseArray with elements of type T. Alias for DenseArray{T,1}.

source

Base.DenseMatrix — Type.

DenseMatrix{T}

Two-dimensional DenseArray with elements of type T. Alias for DenseArray{T,2}.

source

Base.DenseVecOrMat — Constant.

DenseVecOrMat{T}

Union type of DenseVector{T} and DenseMatrix{T}.

source

Base.StridedArray — Constant.

StridedArray{T, N}

An N dimensional strided array with elements of type T. These arrays follow the @ref man-interface-strided-arrays">strided array interface. If A is a StridedArray, then its elements are stored in memory with offsets, which may vary between dimensions but are constant within a dimension. For example, A could have stride 2 in dimension 1, and stride 3 in dimension 2. Incrementing A along dimension d jumps in memory by [strides(A, d)] slots. Strided arrays are particularly important and useful because they can sometimes be passed directly as pointers to foreign language libraries like BLAS.

source

Base.StridedVector — Constant.

StridedVector{T}

One dimensional StridedArray with elements of type T.

source

Base.StridedMatrix — Constant.

StridedMatrix{T}

Two dimensional StridedArray with elements of type T.

source

Base.StridedVecOrMat — Constant.

StridedVecOrMat{T}

Union type of StridedVector and StridedMatrix with elements of type T.

source

Base.getindex — Method.

getindex(type[, elements...])

Construct a 1-d array of the specified type. This is usually called with the syntax Type[]. Element values can be specified using Type[a,b,c,…].

Examples

julia> Int8[1, 2, 3]
3-element Array{Int8,1}:
 1
 2
 3
julia> getindex(Int8, 1, 2, 3)
3-element Array{Int8,1}:
 1
 2
 3

source

Base.zeros — Function.

zeros([T=Float64,] dims...)

Create an Array, with element type T, of all zeros with size specified by dims. See also fill, ones.

Examples

julia> zeros(1)
1-element Array{Float64,1}:
 0.0
julia> zeros(Int8, 2, 3)
2×3 Array{Int8,2}:
 0  0  0
 0  0  0

source

Base.ones — Function.

ones([T=Float64,] dims...)

Create an Array, with element type T, of all ones with size specified by dims. See also: fill, zeros.

Examples

julia> ones(1,2)
1×2 Array{Float64,2}:
 1.0  1.0
julia> ones(ComplexF64, 2, 3)
2×3 Array{Complex{Float64},2}:
 1.0+0.0im  1.0+0.0im  1.0+0.0im
 1.0+0.0im  1.0+0.0im  1.0+0.0im

source

Base.BitArray — Type.

BitArray{N} <: DenseArray{Bool, N}

Space-efficient N-dimensional boolean array, which stores one bit per boolean value.

source

Base.BitArray — Method.

BitArray(undef, dims::Integer...)
BitArray{N}(undef, dims::NTuple{N,Int})

Construct an undef BitArray with the given dimensions. Behaves identically to the Array constructor. See undef.

Examples

julia> BitArray(undef, 2, 2)
2×2 BitArray{2}:
 false  false
 false  true
julia> BitArray(undef, (3, 1))
3×1 BitArray{2}:
 false
 true
 false

source

Base.BitArray — Method.

BitArray(itr)

Construct a BitArray generated by the given iterable object. The shape is inferred from the itr object.

Examples

julia> BitArray([1 0; 0 1])
2×2 BitArray{2}:
  true  false
 false   true
julia> BitArray(x+y == 3 for x = 1:2, y = 1:3)
2×3 BitArray{2}:
 false   true  false
  true  false  false
julia> BitArray(x+y == 3 for x = 1:2 for y = 1:3)
6-element BitArray{1}:
 false
  true
 false
  true
 false
 false

source

Base.trues — Function.

trues(dims)

Create a BitArray with all values set to true.

Examples

julia> trues(2,3)
2×3 BitArray{2}:
 true  true  true
 true  true  true

source

Base.falses — Function.

falses(dims)

Create a BitArray with all values set to false.

Examples

julia> falses(2,3)
2×3 BitArray{2}:
 false  false  false
 false  false  false

source

Base.fill — Function.

fill(x, dims)

Create an array filled with the value x. For example, fill(1.0, (5,5)) returns a 5×5 array of floats, with each element initialized to 1.0.

Examples

julia> fill(1.0, (5,5))
5×5 Array{Float64,2}:
 1.0  1.0  1.0  1.0  1.0
 1.0  1.0  1.0  1.0  1.0
 1.0  1.0  1.0  1.0  1.0
 1.0  1.0  1.0  1.0  1.0
 1.0  1.0  1.0  1.0  1.0

If x is an object reference, all elements will refer to the same object. fill(Foo(), dims) will return an array filled with the result of evaluating Foo() once.

source

Base.fill! — Function.

fill!(A, x)

Fill array A with the value x. If x is an object reference, all elements will refer to the same object. fill!(A, Foo()) will return A filled with the result of evaluating Foo() once.

Examples

julia> A = zeros(2,3)
2×3 Array{Float64,2}:
 0.0  0.0  0.0
 0.0  0.0  0.0
julia> fill!(A, 2.)
2×3 Array{Float64,2}:
 2.0  2.0  2.0
 2.0  2.0  2.0
julia> a = [1, 1, 1]; A = fill!(Vector{Vector{Int}}(undef, 3), a); a[1] = 2; A
3-element Array{Array{Int64,1},1}:
 [2, 1, 1]
 [2, 1, 1]
 [2, 1, 1]
julia> x = 0; f() = (global x += 1; x); fill!(Vector{Int}(undef, 3), f())
3-element Array{Int64,1}:
 1
 1
 1

source

Base.similar — Function.

similar(array, [element_type=eltype(array)], [dims=size(array)])

Create an uninitialized mutable array with the given element type and size, based upon the given source array. The second and third arguments are both optional, defaulting to the given array's eltype and size. The dimensions may be specified either as a single tuple argument or as a series of integer arguments.

Custom AbstractArray subtypes may choose which specific array type is best-suited to return for the given element type and dimensionality. If they do not specialize this method, the default is an Array{element_type}(undef, dims…).

For example, similar(1:10, 1, 4) returns an uninitialized Array{Int,2} since ranges are neither mutable nor support 2 dimensions:

julia> similar(1:10, 1, 4)
1×4 Array{Int64,2}:
 4419743872  4374413872  4419743888  0

Conversely, similar(trues(10,10), 2) returns an uninitialized BitVector with two elements since BitArrays are both mutable and can support 1-dimensional arrays:

julia> similar(trues(10,10), 2)
2-element BitArray{1}:
 false
 false

Since BitArrays can only store elements of type Bool, however, if you request a different element type it will create a regular Array instead:

julia> similar(falses(10), Float64, 2, 4)
2×4 Array{Float64,2}:
 2.18425e-314  2.18425e-314  2.18425e-314  2.18425e-314
 2.18425e-314  2.18425e-314  2.18425e-314  2.18425e-314

source

similar(storagetype, axes)

Create an uninitialized mutable array analogous to that specified by storagetype, but with axes specified by the last argument. storagetype might be a type or a function.

Examples:

similar(Array{Int}, axes(A))

creates an array that "acts like" an Array{Int} (and might indeed be backed by one), but which is indexed identically to A. If A has conventional indexing, this will be identical to Array{Int}(undef, size(A)), but if A has unconventional indexing then the indices of the result will match A.

similar(BitArray, (axes(A, 2),))

would create a 1-dimensional logical array whose indices match those of the columns of A.

source

基础函数

Base.ndims — Function.

ndims(A::AbstractArray) -> Integer

Return the number of dimensions of A.

Examples

julia> A = fill(1, (3,4,5));
julia> ndims(A)
3

source

Base.size — Function.

size(A::AbstractArray, [dim])

Return a tuple containing the dimensions of A. Optionally you can specify a dimension to just get the length of that dimension.

Note that size may not be defined for arrays with non-standard indices, in which case axes may be useful. See the manual chapter on arrays with custom indices.

Examples

julia> A = fill(1, (2,3,4));
julia> size(A)
(2, 3, 4)
julia> size(A, 2)
3

source

Base.axes — Method.

axes(A)

Return the tuple of valid indices for array A.

Examples

julia> A = fill(1, (5,6,7));
julia> axes(A)
(Base.OneTo(5), Base.OneTo(6), Base.OneTo(7))

source

Base.axes — Method.

axes(A, d)

Return the valid range of indices for array A along dimension d.

See also size, and the manual chapter on arrays with custom indices.

Examples

julia> A = fill(1, (5,6,7));
julia> axes(A, 2)
Base.OneTo(6)

source

Base.length — Method.

length(A::AbstractArray)

Return the number of elements in the array, defaults to prod(size(A)).

Examples

julia> length([1, 2, 3, 4])
4
julia> length([1 2; 3 4])
4

source

Base.eachindex — Function.

eachindex(A...)

Create an iterable object for visiting each index of an AbstractArray A in an efficient manner. For array types that have opted into fast linear indexing (like Array), this is simply the range 1:length(A). For other array types, return a specialized Cartesian range to efficiently index into the array with indices specified for every dimension. For other iterables, including strings and dictionaries, return an iterator object supporting arbitrary index types (e.g. unevenly spaced or non-integer indices).

If you supply more than one AbstractArray argument, eachindex will create an iterable object that is fast for all arguments (a UnitRange if all inputs have fast linear indexing, a CartesianIndices otherwise). If the arrays have different sizes and/or dimensionalities, eachindex will return an iterable that spans the largest range along each dimension.

Examples

julia> A = [1 2; 3 4];
julia> for i in eachindex(A) # linear indexing
           println(i)
       end
1
2
3
4
julia> for i in eachindex(view(A, 1:2, 1:1)) # Cartesian indexing
           println(i)
       end
CartesianIndex(1, 1)
CartesianIndex(2, 1)

source

Base.IndexStyle — Type.

IndexStyle(A)
IndexStyle(typeof(A))

IndexStyle specifies the "native indexing style" for array A. When you define a new AbstractArray type, you can choose to implement either linear indexing or cartesian indexing. If you decide to implement linear indexing, then you must set this trait for your array type:

Base.IndexStyle(::Type{<:MyArray}) = IndexLinear()

The default is IndexCartesian().

Julia's internal indexing machinery will automatically (and invisibly) convert all indexing operations into the preferred style. This allows users to access elements of your array using any indexing style, even when explicit methods have not been provided.

If you define both styles of indexing for your AbstractArray, this trait can be used to select the most performant indexing style. Some methods check this trait on their inputs, and dispatch to different algorithms depending on the most efficient access pattern. In particular, eachindex creates an iterator whose type depends on the setting of this trait.

source

Base.conj! — Function.

conj!(A)

Transform an array to its complex conjugate in-place.

See also conj.

Examples

julia> A = [1+im 2-im; 2+2im 3+im]
2×2 Array{Complex{Int64},2}:
 1+1im  2-1im
 2+2im  3+1im
julia> conj!(A);
julia> A
2×2 Array{Complex{Int64},2}:
 1-1im  2+1im
 2-2im  3-1im

source

Base.stride — Function.

stride(A, k::Integer)

Return the distance in memory (in number of elements) between adjacent elements in dimension k.

Examples

julia> A = fill(1, (3,4,5));
julia> stride(A,2)
3
julia> stride(A,3)
12

source

Base.strides — Function.

strides(A)

Return a tuple of the memory strides in each dimension.

Examples

julia> A = fill(1, (3,4,5));
julia> strides(A)
(1, 3, 12)

source

广播与矢量化

也可参照 dot syntax for vectorizing functions； 例如，f.(args…) 隐式调用 broadcast(f, args…)。 与其依赖如 sin 函数的“已矢量化”方法，你应该使用 sin.(a) 来使用broadcast来矢量化。

Base.Broadcast.broadcast — Function.

broadcast(f, As...)

Broadcast the function f over the arrays, tuples, collections, Refs and/or scalars As.

Broadcasting applies the function f over the elements of the container arguments and the scalars themselves in As. Singleton and missing dimensions are expanded to match the extents of the other arguments by virtually repeating the value. By default, only a limited number of types are considered scalars, including Numbers, Strings, Symbols, Types, Functions and some common singletons like missing and nothing. All other arguments are iterated over or indexed into elementwise.

The resulting container type is established by the following rules:

• If all the arguments are scalars or zero-dimensional arrays, it returns an unwrapped scalar.
• If at least one argument is a tuple and all others are scalars or zero-dimensional arrays, it returns a tuple.
• All other combinations of arguments default to returning an Array, but custom container types can define their own implementation and promotion-like rules to customize the result when they appear as arguments.
  A special syntax exists for broadcasting: f.(args…) is equivalent to broadcast(f, args…), and nested f.(g.(args…)) calls are fused into a single broadcast loop.

Examples

julia> A = [1, 2, 3, 4, 5]
5-element Array{Int64,1}:
 1
 2
 3
 4
 5
julia> B = [1 2; 3 4; 5 6; 7 8; 9 10]
5×2 Array{Int64,2}:
 1   2
 3   4
 5   6
 7   8
 9  10
julia> broadcast(+, A, B)
5×2 Array{Int64,2}:
  2   3
  5   6
  8   9
 11  12
 14  15
julia> parse.(Int, ["1", "2"])
2-element Array{Int64,1}:
 1
 2
julia> abs.((1, -2))
(1, 2)
julia> broadcast(+, 1.0, (0, -2.0))
(1.0, -1.0)
julia> (+).([[0,2], [1,3]], Ref{Vector{Int}}([1,-1]))
2-element Array{Array{Int64,1},1}:
 [1, 1]
 [2, 2]
julia> string.(("one","two","three","four"), ": ", 1:4)
4-element Array{String,1}:
 "one: 1"
 "two: 2"
 "three: 3"
 "four: 4"

source

Base.Broadcast.broadcast! — Function.

broadcast!(f, dest, As...)

Like broadcast, but store the result of broadcast(f, As…) in the dest array. Note that dest is only used to store the result, and does not supply arguments to f unless it is also listed in the As, as in broadcast!(f, A, A, B) to perform A[:] = broadcast(f, A, B).

source

@__dot__">Base.Broadcast.@dot — Macro.

@. expr

Convert every function call or operator in expr into a "dot call" (e.g. convert f(x) to f.(x)), and convert every assignment in expr to a "dot assignment" (e.g. convert += to .+=).

If you want to avoid adding dots for selected function calls in expr, splice those function calls in with $. For example, @. sqrt(abs($sort(x))) is equivalent to sqrt.(abs.(sort(x))) (no dot for sort).

(@. is equivalent to a call to @dot.)

Examples

julia> x = 1.0:3.0; y = similar(x);
julia> @. y = x + 3 * sin(x)
3-element Array{Float64,1}:
 3.5244129544236893
 4.727892280477045
 3.4233600241796016

source

自定义类型的广播，请参照

Base.Broadcast.BroadcastStyle — Type.

BroadcastStyle is an abstract type and trait-function used to determine behavior of objects under broadcasting. BroadcastStyle(typeof(x)) returns the style associated with x. To customize the broadcasting behavior of a type, one can declare a style by defining a type/method pair

struct MyContainerStyle <: BroadcastStyle end
Base.BroadcastStyle(::Type{<:MyContainer}) = MyContainerStyle()

One then writes method(s) (at least similar) operating on Broadcasted{MyContainerStyle}. There are also several pre-defined subtypes of BroadcastStyle that you may be able to leverage; see the @ref man-interfaces-broadcasting">Interfaces chapter for more information.

source

Base.Broadcast.broadcast_axes — Function.

Base.broadcast_axes(A)

Compute the axes for A.

This should only be specialized for objects that do not define axes but want to participate in broadcasting.

source

Base.Broadcast.AbstractArrayStyle — Type.

Broadcast.AbstractArrayStyle{N} <: BroadcastStyle is the abstract supertype for any style associated with an AbstractArray type. The N parameter is the dimensionality, which can be handy for AbstractArray types that only support specific dimensionalities:

struct SparseMatrixStyle <: Broadcast.AbstractArrayStyle{2} end
Base.BroadcastStyle(::Type{<:SparseMatrixCSC}) = SparseMatrixStyle()

For AbstractArray types that support arbitrary dimensionality, N can be set to Any:

struct MyArrayStyle <: Broadcast.AbstractArrayStyle{Any} end
Base.BroadcastStyle(::Type{<:MyArray}) = MyArrayStyle()

In cases where you want to be able to mix multiple AbstractArrayStyles and keep track of dimensionality, your style needs to support a Val constructor:

struct MyArrayStyleDim{N} <: Broadcast.AbstractArrayStyle{N} end
(::Type{<:MyArrayStyleDim})(::Val{N}) where N = MyArrayStyleDim{N}()

Note that if two or more AbstractArrayStyle subtypes conflict, broadcasting machinery will fall back to producing Arrays. If this is undesirable, you may need to define binary BroadcastStyle rules to control the output type.

See also Broadcast.DefaultArrayStyle.

source

Base.Broadcast.ArrayStyle — Type.

Broadcast.ArrayStyle{MyArrayType}() is a BroadcastStyle indicating that an object behaves as an array for broadcasting. It presents a simple way to construct Broadcast.AbstractArrayStyles for specific AbstractArray container types. Broadcast styles created this way lose track of dimensionality; if keeping track is important for your type, you should create your own custom Broadcast.AbstractArrayStyle.

source

Base.Broadcast.DefaultArrayStyle — Type.

Broadcast.DefaultArrayStyle{N}() is a BroadcastStyle indicating that an object behaves as an N-dimensional array for broadcasting. Specifically, DefaultArrayStyle is used for any AbstractArray type that hasn't defined a specialized style, and in the absence of overrides from other broadcast arguments the resulting output type is Array. When there are multiple inputs to broadcast, DefaultArrayStyle "loses" to any other Broadcast.ArrayStyle.

source

Base.Broadcast.broadcastable — Function.

Broadcast.broadcastable(x)

Return either x or an object like x such that it supports axes, indexing, and its type supports ndims.

If x supports iteration, the returned value should have the same axes and indexing behaviors as collect(x).

If x is not an AbstractArray but it supports axes, indexing, and its type supports ndims, then broadcastable(::typeof(x)) may be implemented to just return itself. Further, if x defines its own BroadcastStyle, then it must define its broadcastable method to return itself for the custom style to have any effect.

Examples

julia> Broadcast.broadcastable([1,2,3]) # like `identity` since arrays already support axes and indexing
3-element Array{Int64,1}:
 1
 2
 3
julia> Broadcast.broadcastable(Int) # Types don't support axes, indexing, or iteration but are commonly used as scalars
Base.RefValue{Type{Int64}}(Int64)
julia> Broadcast.broadcastable("hello") # Strings break convention of matching iteration and act like a scalar instead
Base.RefValue{String}("hello")

source

索引与赋值

Base.getindex — Method.

getindex(A, inds...)

Return a subset of array A as specified by inds, where each ind may be an Int, an AbstractRange, or a Vector. See the manual section on array indexing for details.

Examples

julia> A = [1 2; 3 4]
2×2 Array{Int64,2}:
 1  2
 3  4
julia> getindex(A, 1)
1
julia> getindex(A, [2, 1])
2-element Array{Int64,1}:
 3
 1
julia> getindex(A, 2:4)
3-element Array{Int64,1}:
 3
 2
 4

source

Base.setindex! — Method.

setindex!(A, X, inds...)
A[inds...] = X

Store values from array X within some subset of A as specified by inds. The syntax A[inds…] = X is equivalent to setindex!(A, X, inds…).

Examples

julia> A = zeros(2,2);
julia> setindex!(A, [10, 20], [1, 2]);
julia> A[[3, 4]] = [30, 40];
julia> A
2×2 Array{Float64,2}:
 10.0  30.0
 20.0  40.0

source

Base.copyto! — Method.

copyto!(dest, Rdest::CartesianIndices, src, Rsrc::CartesianIndices) -> dest

Copy the block of src in the range of Rsrc to the block of dest in the range of Rdest. The sizes of the two regions must match.

source

Base.isassigned — Function.

isassigned(array, i) -> Bool

Test whether the given array has a value associated with index i. Return false if the index is out of bounds, or has an undefined reference.

Examples

julia> isassigned(rand(3, 3), 5)
true
julia> isassigned(rand(3, 3), 3 * 3 + 1)
false
julia> mutable struct Foo end
julia> v = similar(rand(3), Foo)
3-element Array{Foo,1}:
 #undef
 #undef
 #undef
julia> isassigned(v, 1)
false

source

Base.Colon — Type.

Colon()

Colons (:) are used to signify indexing entire objects or dimensions at once.

Very few operations are defined on Colons directly; instead they are converted by to_indices to an internal vector type (Base.Slice) to represent the collection of indices they span before being used.

The singleton instance of Colon is also a function used to construct ranges; see :.

source

Base.IteratorsMD.CartesianIndex — Type.

CartesianIndex(i, j, k...)   -> I
CartesianIndex((i, j, k...)) -> I

Create a multidimensional index I, which can be used for indexing a multidimensional array A. In particular, A[I] is equivalent to A[i,j,k…]. One can freely mix integer and CartesianIndex indices; for example, A[Ipre, i, Ipost] (where Ipre and Ipost are CartesianIndex indices and i is an Int) can be a useful expression when writing algorithms that work along a single dimension of an array of arbitrary dimensionality.

A CartesianIndex is sometimes produced by eachindex, and always when iterating with an explicit CartesianIndices.

Examples

julia> A = reshape(Vector(1:16), (2, 2, 2, 2))
2×2×2×2 Array{Int64,4}:
[:, :, 1, 1] =
 1  3
 2  4
[:, :, 2, 1] =
 5  7
 6  8
[:, :, 1, 2] =
  9  11
 10  12
[:, :, 2, 2] =
 13  15
 14  16
julia> A[CartesianIndex((1, 1, 1, 1))]
1
julia> A[CartesianIndex((1, 1, 1, 2))]
9
julia> A[CartesianIndex((1, 1, 2, 1))]
5

source

Base.IteratorsMD.CartesianIndices — Type.

CartesianIndices(sz::Dims) -> R
CartesianIndices(istart:istop, jstart:jstop, ...) -> R

Define a region R spanning a multidimensional rectangular range of integer indices. These are most commonly encountered in the context of iteration, where for I in R … end will return CartesianIndex indices I equivalent to the nested loops

for j = jstart:jstop
    for i = istart:istop
        ...
    end
end

Consequently these can be useful for writing algorithms that work in arbitrary dimensions.

CartesianIndices(A::AbstractArray) -> R

As a convenience, constructing a CartesianIndices from an array makes a range of its indices.

Examples

julia> foreach(println, CartesianIndices((2, 2, 2)))
CartesianIndex(1, 1, 1)
CartesianIndex(2, 1, 1)
CartesianIndex(1, 2, 1)
CartesianIndex(2, 2, 1)
CartesianIndex(1, 1, 2)
CartesianIndex(2, 1, 2)
CartesianIndex(1, 2, 2)
CartesianIndex(2, 2, 2)
julia> CartesianIndices(fill(1, (2,3)))
2×3 CartesianIndices{2,Tuple{Base.OneTo{Int64},Base.OneTo{Int64}}}:
 CartesianIndex(1, 1)  CartesianIndex(1, 2)  CartesianIndex(1, 3)
 CartesianIndex(2, 1)  CartesianIndex(2, 2)  CartesianIndex(2, 3)

Conversion between linear and cartesian indices

Linear index to cartesian index conversion exploits the fact that a CartesianIndices is an AbstractArray and can be indexed linearly:

julia> cartesian = CartesianIndices((1:3, 1:2))
3×2 CartesianIndices{2,Tuple{UnitRange{Int64},UnitRange{Int64}}}:
 CartesianIndex(1, 1)  CartesianIndex(1, 2)
 CartesianIndex(2, 1)  CartesianIndex(2, 2)
 CartesianIndex(3, 1)  CartesianIndex(3, 2)
julia> cartesian[4]
CartesianIndex(1, 2)

For cartesian to linear index conversion, see LinearIndices.

source

Base.Dims — Type.

Dims{N}

An NTuple of N Ints used to represent the dimensions of an AbstractArray.

source

Base.LinearIndices — Type.

LinearIndices(A::AbstractArray)

Return a LinearIndices array with the same shape and axes as A, holding the linear index of each entry in A. Indexing this array with cartesian indices allows mapping them to linear indices.

For arrays with conventional indexing (indices start at 1), or any multidimensional array, linear indices range from 1 to length(A). However, for AbstractVectors linear indices are axes(A, 1), and therefore do not start at 1 for vectors with unconventional indexing.

Calling this function is the "safe" way to write algorithms that exploit linear indexing.

Examples

julia> A = fill(1, (5,6,7));
julia> b = LinearIndices(A);
julia> extrema(b)
(1, 210)

LinearIndices(inds::CartesianIndices) -> R
LinearIndices(sz::Dims) -> R
LinearIndices(istart:istop, jstart:jstop, ...) -> R

Return a LinearIndices array with the specified shape or axes.

Example

The main purpose of this constructor is intuitive conversion from cartesian to linear indexing:

julia> linear = LinearIndices((1:3, 1:2))
3×2 LinearIndices{2,Tuple{UnitRange{Int64},UnitRange{Int64}}}:
 1  4
 2  5
 3  6
julia> linear[1,2]
4

source

Base.to_indices — Function.

to_indices(A, I::Tuple)

Convert the tuple I to a tuple of indices for use in indexing into array A.

The returned tuple must only contain either Ints or AbstractArrays of scalar indices that are supported by array A. It will error upon encountering a novel index type that it does not know how to process.

For simple index types, it defers to the unexported Base.to_index(A, i) to process each index i. While this internal function is not intended to be called directly, Base.to_index may be extended by custom array or index types to provide custom indexing behaviors.

More complicated index types may require more context about the dimension into which they index. To support those cases, to_indices(A, I) calls to_indices(A, axes(A), I), which then recursively walks through both the given tuple of indices and the dimensional indices of A in tandem. As such, not all index types are guaranteed to propagate to Base.to_index.

source

Base.checkbounds — Function.

checkbounds(Bool, A, I...)

Return true if the specified indices I are in bounds for the given array A. Subtypes of AbstractArray should specialize this method if they need to provide custom bounds checking behaviors; however, in many cases one can rely on A's indices and checkindex.

See also checkindex.

Examples

julia> A = rand(3, 3);
julia> checkbounds(Bool, A, 2)
true
julia> checkbounds(Bool, A, 3, 4)
false
julia> checkbounds(Bool, A, 1:3)
true
julia> checkbounds(Bool, A, 1:3, 2:4)
false

source

checkbounds(A, I...)

Throw an error if the specified indices I are not in bounds for the given array A.

source

Base.checkindex — Function.

checkindex(Bool, inds::AbstractUnitRange, index)

Return true if the given index is within the bounds of inds. Custom types that would like to behave as indices for all arrays can extend this method in order to provide a specialized bounds checking implementation.

Examples

julia> checkindex(Bool, 1:20, 8)
true
julia> checkindex(Bool, 1:20, 21)
false

source

Views (SubArrays 以及其它 view 类型)

Base.view — Function.

view(A, inds...)

Like getindex, but returns a view into the parent array A with the given indices instead of making a copy. Calling getindex or setindex! on the returned SubArray computes the indices to the parent array on the fly without checking bounds.

Examples

julia> A = [1 2; 3 4]
2×2 Array{Int64,2}:
 1  2
 3  4
julia> b = view(A, :, 1)
2-element view(::Array{Int64,2}, :, 1) with eltype Int64:
 1
 3
julia> fill!(b, 0)
2-element view(::Array{Int64,2}, :, 1) with eltype Int64:
 0
 0
julia> A # Note A has changed even though we modified b
2×2 Array{Int64,2}:
 0  2
 0  4

source

Base.@view — Macro.

@view A[inds...]

Creates a SubArray from an indexing expression. This can only be applied directly to a reference expression (e.g. @view A[1,2:end]), and should not be used as the target of an assignment (e.g. @view(A[1,2:end]) = …). See also @views"">@views to switch an entire block of code to use views for slicing.

Examples

julia> A = [1 2; 3 4]
2×2 Array{Int64,2}:
 1  2
 3  4
julia> b = @view A[:, 1]
2-element view(::Array{Int64,2}, :, 1) with eltype Int64:
 1
 3
julia> fill!(b, 0)
2-element view(::Array{Int64,2}, :, 1) with eltype Int64:
 0
 0
julia> A
2×2 Array{Int64,2}:
 0  2
 0  4

source

Base.@views — Macro.

@views expression

Convert every array-slicing operation in the given expression (which may be a begin/end block, loop, function, etc.) to return a view. Scalar indices, non-array types, and explicit getindex calls (as opposed to array[…]) are unaffected.

Note

The @views macro only affects array[…] expressions that appear explicitly in the given expression, not array slicing that occurs in functions called by that code.

Examples

julia> A = zeros(3, 3);
julia> @views for row in 1:3
           b = A[row, :]
           b[:] .= row
       end
julia> A
3×3 Array{Float64,2}:
 1.0  1.0  1.0
 2.0  2.0  2.0
 3.0  3.0  3.0

source

Base.parent — Function.

parent(A)

Returns the "parent array" of an array view type (e.g., SubArray), or the array itself if it is not a view.

Examples

julia> A = [1 2; 3 4]
2×2 Array{Int64,2}:
 1  2
 3  4
julia> V = view(A, 1:2, :)
2×2 view(::Array{Int64,2}, 1:2, :) with eltype Int64:
 1  2
 3  4
julia> parent(V)
2×2 Array{Int64,2}:
 1  2
 3  4

source

Base.parentindices — Function.

parentindices(A)

From an array view A, returns the corresponding indices in the parent.

source

Base.selectdim — Function.

selectdim(A, d::Integer, i)

Return a view of all the data of A where the index for dimension d equals i.

Equivalent to view(A,:,:,…,i,:,:,…) where i is in position d.

Examples

julia> A = [1 2 3 4; 5 6 7 8]
2×4 Array{Int64,2}:
 1  2  3  4
 5  6  7  8
julia> selectdim(A, 2, 3)
2-element view(::Array{Int64,2}, :, 3) with eltype Int64:
 3
 7

source

Base.reinterpret — Function.

reinterpret(type, A)

Change the type-interpretation of a block of memory. For arrays, this constructs a view of the array with the same binary data as the given array, but with the specified element type. For example, reinterpret(Float32, UInt32(7)) interprets the 4 bytes corresponding to UInt32(7) as a Float32.

Examples

julia> reinterpret(Float32, UInt32(7))
1.0f-44
julia> reinterpret(Float32, UInt32[1 2 3 4 5])
1×5 reinterpret(Float32, ::Array{UInt32,2}):
 1.4013e-45  2.8026e-45  4.2039e-45  5.60519e-45  7.00649e-45

source

Base.reshape — Function.

reshape(A, dims...) -> AbstractArray
reshape(A, dims) -> AbstractArray

Return an array with the same data as A, but with different dimension sizes or number of dimensions. The two arrays share the same underlying data, so that the result is mutable if and only if A is mutable, and setting elements of one alters the values of the other.

The new dimensions may be specified either as a list of arguments or as a shape tuple. At most one dimension may be specified with a :, in which case its length is computed such that its product with all the specified dimensions is equal to the length of the original array A. The total number of elements must not change.

Examples

julia> A = Vector(1:16)
16-element Array{Int64,1}:
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
julia> reshape(A, (4, 4))
4×4 Array{Int64,2}:
 1  5   9  13
 2  6  10  14
 3  7  11  15
 4  8  12  16
julia> reshape(A, 2, :)
2×8 Array{Int64,2}:
 1  3  5  7   9  11  13  15
 2  4  6  8  10  12  14  16
julia> reshape(1:6, 2, 3)
2×3 reshape(::UnitRange{Int64}, 2, 3) with eltype Int64:
 1  3  5
 2  4  6

source

Base.dropdims — Function.

dropdims(A; dims)

Remove the dimensions specified by dims from array A. Elements of dims must be unique and within the range 1:ndims(A). size(A,i) must equal 1 for all i in dims.

Examples

julia> a = reshape(Vector(1:4),(2,2,1,1))
2×2×1×1 Array{Int64,4}:
[:, :, 1, 1] =
 1  3
 2  4
julia> dropdims(a; dims=3)
2×2×1 Array{Int64,3}:
[:, :, 1] =
 1  3
 2  4

source

Base.vec — Function.

vec(a::AbstractArray) -> AbstractVector

Reshape the array a as a one-dimensional column vector. Return a if it is already an AbstractVector. The resulting array shares the same underlying data as a, so it will only be mutable if a is mutable, in which case modifying one will also modify the other.

Examples

julia> a = [1 2 3; 4 5 6]
2×3 Array{Int64,2}:
 1  2  3
 4  5  6
julia> vec(a)
6-element Array{Int64,1}:
 1
 4
 2
 5
 3
 6
julia> vec(1:3)
1:3

See also reshape.

source

级联与置换

Base.cat — Function.

cat(A...; dims=dims)

Concatenate the input arrays along the specified dimensions in the iterable dims. For dimensions not in dims, all input arrays should have the same size, which will also be the size of the output array along that dimension. For dimensions in dims, the size of the output array is the sum of the sizes of the input arrays along that dimension. If dims is a single number, the different arrays are tightly stacked along that dimension. If dims is an iterable containing several dimensions, this allows one to construct block diagonal matrices and their higher-dimensional analogues by simultaneously increasing several dimensions for every new input array and putting zero blocks elsewhere. For example, cat(matrices…; dims=(1,2)) builds a block diagonal matrix, i.e. a block matrix with matrices[1], matrices[2], … as diagonal blocks and matching zero blocks away from the diagonal.

source

Base.vcat — Function.

vcat(A...)

Concatenate along dimension 1.

Examples

julia> a = [1 2 3 4 5]
1×5 Array{Int64,2}:
 1  2  3  4  5
julia> b = [6 7 8 9 10; 11 12 13 14 15]
2×5 Array{Int64,2}:
  6   7   8   9  10
 11  12  13  14  15
julia> vcat(a,b)
3×5 Array{Int64,2}:
  1   2   3   4   5
  6   7   8   9  10
 11  12  13  14  15
julia> c = ([1 2 3], [4 5 6])
([1 2 3], [4 5 6])
julia> vcat(c...)
2×3 Array{Int64,2}:
 1  2  3
 4  5  6

source

Base.hcat — Function.

hcat(A...)

Concatenate along dimension 2.

Examples

julia> a = [1; 2; 3; 4; 5]
5-element Array{Int64,1}:
 1
 2
 3
 4
 5
julia> b = [6 7; 8 9; 10 11; 12 13; 14 15]
5×2 Array{Int64,2}:
  6   7
  8   9
 10  11
 12  13
 14  15
julia> hcat(a,b)
5×3 Array{Int64,2}:
 1   6   7
 2   8   9
 3  10  11
 4  12  13
 5  14  15
julia> c = ([1; 2; 3], [4; 5; 6])
([1, 2, 3], [4, 5, 6])
julia> hcat(c...)
3×2 Array{Int64,2}:
 1  4
 2  5
 3  6