在给定索引的切片中插入值 [英] Insert a value in a slice at a given index

问题描述

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array1 := []int{1, 3, 4, 5}
array2 := []int{2, 4, 6, 8}

我想在 array1 [1] 即 3 之前插入 array2 [2] 即 6 array1 变成 {1、6、3、4、5} 的一部分.我该怎么办?

I want to insert array2[2] i.e 6 at array1[1] i.e before 3 so that array1 becomes a slice of {1, 6, 3, 4, 5}. How can I do it?

我在线阅读的大多数技术都涉及到使用:运算符，但也会导致剩余元素也被插入.如何在切片的索引处附加单个值?

Most the techniques I read online involve using the : operator but results in remaining elements being inserted as well. How can I append single values at an index in a slice?

推荐答案

简单，高效且合乎逻辑的方式:

Simple, efficient and logical way:

1. 确保 array1 具有足够的容量(长度)以容纳新的可插入元素.为此，请使用内置的 append() (这无关紧要，它将被覆盖).
2. 要插入元素，必须对现有元素进行移位(复制到更高的1个索引)以为该元素腾出空间，例如使用内置的 copy() (要插入的元素).
3. 使用单个分配将元素设置为正确的索引.

1. Make sure array1 has enough capacity (length) to accomodate the new, insertable element. To do that, append a single element using the builting append() (doesn't matter what that is, it'll get overwritten).
2. To insert an element, existing elements must be shifted (copied over to 1 index higher) to make room for that element, e.g. using the builtin copy() (elements you want to insert before).
3. Set the element at the proper index, using a single assignment.

在代码中:

array1 := []int{1, 3, 4, 5}
array2 := []int{2, 4, 6, 8}

array1 = append(array1, 0)   // Step 1
copy(array1[2:], array1[1:]) // Step 2
array1[1] = array2[2]        // Step 3

fmt.Println(array1)

输出(在转到游乐场上尝试):

[1 6 3 4 5]

特殊情况下的优化

请注意，在某些特殊情况下(当slice元素很大时，就像一个大结构)，附加最后一个元素可能会更快，然后复制少于1个元素就足够了(因为附加的最后一个元素是正确的的位置.

Optimization in special cases

Note that in some special cases (when the slice element is big, like a big struct), it may be faster to append the last element, and then it's enough to copy 1 less elements (because the appended last element is right where it needs to be).

它是这样的:

last := len(array1) - 1
array1 = append(array1, array1[last]) // Step 1
copy(array1[2:], array1[1:last])      // Step 2
array1[1] = array2[2]                 // Step 3

这将导致相同的切片.在去游乐场上尝试一下.

This will result in the same slice. Try this one on the Go Playground.

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