Question

有没有办法在Julia中使用for循环中的previous和next值进行操作？我无法从Julia文档中找到任何答案。

示例：

List1 = ["a", "b", "c"]
for letter in List1
   println(previous letter)
end

这个循环会给＆＃34; a＆＃34;因此，当它在＆＃34; b＆＃34;等上运行时

Answer 1

不要让简单的事情复杂化：

List1 = ["a", "b", "c"]

for i = 2:length(List1)
    println("The previous letter of $(List1[i]) is $(List1[i-1])")
end

输出：

The previous letter of b is a
The previous letter of c is b

Answer 2

另一种方法是使用IterTools.jl包中的partition迭代器：

using IterTools

List1 = ["a", "b", "c"];
for (prev,next) in partition(List1,2,1)
    @show prev
end

给出：

prev = "a"
prev = "b"

next具有当前迭代的值（即"b"和"c"），循环跳过第一个值的迭代（没有prev）。< / p>

Answer 3

您可以使用enumerate函数获取上一个索引，例如：

julia> list1 = ["a", "b", "c"]
3-element Array{String,1}:
 "a"
 "b"
 "c"

julia> enumerate(list1)
Enumerate{Array{String,1}}(["a", "b", "c"])

julia> collect(ans)
3-element Array{Tuple{Int64,String},1}:
 (1, "a")
 (2, "b")
 (3, "c")

julia> function prev(list::Vector{String})
           enumeration = enumerate(list)
           for (index, element) in enumeration
               if index == 1
                   continue
               else
                   println("The previous letter of $element is $(list[index - 1]).")
               end
           end
       end
prev (generic function with 1 method)

julia> prev(list1)
The previous letter of b is a.
The previous letter of c is b.

Answer 4

我想我找到了一种自己做的方法：

List1 = ["a", "b", "c"]
for letter in List1
    if  !(findn(List1 .== letter) == [1])
        println("The previous letter of ", letter, " is ", List1[findn(List1 .== letter)-1])
    end
end

输出：

The previous letter of b is String["a"]
The previous letter of c is String["b"]

现在唯一的问题是结果是某种字符串数组。

Julia - for循环中的上一个和下一个值

4 个答案: