排序及相关函数

排序及相关函数

Julia 拥有为数众多的灵活的 API，用于对已经排序的值数组进行排序和交互。默认情况下，Julia 会选择合理的算法并按标准升序进行排序：

julia> sort([2,3,1])
3-element Vector{Int64}:
 1
 2
 3

你同样可以轻松实现逆序排序：

julia> sort([2,3,1], rev=true)
3-element Vector{Int64}:
 3
 2
 1

对数组进行 in-place 排序时，要使用 ! 版的排序函数：

julia> a = [2,3,1];
julia> sort!(a);
julia> a
3-element Vector{Int64}:
 1
 2
 3

你可以计算用于排列的索引，而不是直接对数组进行排序：

julia> v = randn(5)
5-element Array{Float64,1}:
  0.297288
  0.382396
 -0.597634
 -0.0104452
 -0.839027
julia> p = sortperm(v)
5-element Array{Int64,1}:
 5
 3
 4
 1
 2
julia> v[p]
5-element Array{Float64,1}:
 -0.839027
 -0.597634
 -0.0104452
  0.297288
  0.382396

数组可以根据对其值任意的转换结果来进行排序；

julia> sort(v, by=abs)
5-element Array{Float64,1}:
 -0.0104452
  0.297288
  0.382396
 -0.597634
 -0.839027

或者通过转换来进行逆序排序

julia> sort(v, by=abs, rev=true)
5-element Array{Float64,1}:
 -0.839027
 -0.597634
  0.382396
  0.297288
 -0.0104452

如有必要，可以选择排序算法：

julia> sort(v, alg=InsertionSort)
5-element Array{Float64,1}:
 -0.839027
 -0.597634
 -0.0104452
  0.297288
  0.382396

所有与排序和顺序相关的函数依赖于“小于”关系，该关系定义了要操纵的值的总顺序。默认情况下会调用 isless 函数，但可以通过 lt 关键字指定关系。

排序函数

Base.sort! — Function

sort!(v; alg::Algorithm=defalg(v), lt=isless, by=identity, rev::Bool=false, order::Ordering=Forward)

Sort the vector v in place. QuickSort is used by default for numeric arrays while MergeSort is used for other arrays. You can specify an algorithm to use via the alg keyword (see Sorting Algorithms for available algorithms). The by keyword lets you provide a function that will be applied to each element before comparison; the lt keyword allows providing a custom “less than” function (note that for every x and y, only one of lt(x,y) and lt(y,x) can return true); use rev=true to reverse the sorting order. These options are independent and can be used together in all possible combinations: if both by and lt are specified, the lt function is applied to the result of the by function; rev=true reverses whatever ordering specified via the by and lt keywords.

Examples

julia> v = [3, 1, 2]; sort!(v); v
3-element Vector{Int64}:
 1
 2
 3
julia> v = [3, 1, 2]; sort!(v, rev = true); v
3-element Vector{Int64}:
 3
 2
 1
julia> v = [(1, "c"), (3, "a"), (2, "b")]; sort!(v, by = x -> x[1]); v
3-element Vector{Tuple{Int64, String}}:
 (1, "c")
 (2, "b")
 (3, "a")
julia> v = [(1, "c"), (3, "a"), (2, "b")]; sort!(v, by = x -> x[2]); v
3-element Vector{Tuple{Int64, String}}:
 (3, "a")
 (2, "b")
 (1, "c")

排序及相关函数

排序及相关函数

排序函数

排列顺序相关的函数

排序算法

Alternate orderings