golang slice delete

In Golang, slice is a very practical data structure. It is very similar to an array, but can be expanded and contracted dynamically. However, when we need to delete an element from the slice, some additional operations may be required. This article will explain how to use slice in Golang to delete an element.

In Golang, slice is created by using the make function. For example, the code shown below will create a slice containing three initial values:

a := make([]int, 3)
a[0] = 1
a[1] = 2
a[2] = 3

Now, we have a slice of length 3, which contains three integers: 1, 2, 3. Let's imagine that we want to delete the second element in this slice, which is 2.

First, let us take a look at the "append" function provided in Golang. It allows us to add one or more elements at the end of the slice. This is a very convenient function that we can use to implement deletion operations. Specifically, we can use the append function to remove an element from a slice and then return a new slice that does not contain the removed element.

Let's look at an example:

a := []int{1, 2, 3}
a = append(a[:1], a[2:]...)
fmt.Println(a) // 输出 [1, 3]

In this example, we first declare an initial slice, and then use the append function to delete the second element of the slice. In this example, we use the slice operator [:] to select a portion of the slice. a[:1] means starting from the starting position of the slice (0) and ending at the first position (1). a[2:] means starting from the third position (2) and ending at the end of the slice. Finally, we reassemble these two "half slices" into a new slice that does not contain the second element (i.e. 2).

It should be noted that we use the "..." operator when calling the append function. This is syntactic sugar in Golang that allows us to "unpack" a slice into separate elements. Therefore, a[2:]... can be unpacked to 3. In addition, we need to assign the result of the append function back to the original slice a, otherwise our operation will not have any impact on the original slice.

Although this method can achieve our purpose, it has a disadvantage: every time we delete an element, we need to reallocate a new slice. This approach can become very inefficient if we need to delete multiple elements in a large slice. So, in some cases, we may need to use another way to remove elements.

Another way to delete slice elements in Golang is to use the built-in copy function. Unlike using "append", using the copy function does not require reallocating a new slice. Instead, we can use the copy function to move the elements in the slice forward and then omit the elements to be deleted. Specifically, we can replace the element to be deleted with the last element of the slice and then move the pointer to the slice backward. In this way, we can "overwrite" the elements to be deleted and keep the order of all elements in the slice correct. We can then simply reduce the length of the slice by 1 to remove the last element (which has been copied to the location of the removed element).

The following is an example of using the copy function to delete slice elements:

a := []int{1, 2, 3}
i := 1
copy(a[i:], a[i+1:])
a[len(a)-1] = 0 // 或 a = a[:len(a)-1]
fmt.Println(a) // 输出 [1, 3, 0]

In this example, we first declare an initial slice, and the index of the element to be deleted is 1 (in In the slice, the index of the second element is 1). We then called the copy function to move the remainder of the slice (starting from the second element) forward one position to cover the element to be deleted. Finally, we reduce the length of the slice by 1 and set the last element to 0, or we can use a = a[:len(a)-1] to completely remove the last element.

Note The thing is, when using the copy function, we must explicitly specify the number of elements to be copied in the slice. In this example, we use a[i 1:] to select starting from the element next to the element to be deleted and ending at the end of the slice. This selection includes the last element, since we will set its value to 0 (or remove it) in the next step.

This article introduces two methods to delete slice elements in Golang. The first method uses the "append" function, while the second method uses the "copy" function. Although both methods can effectively delete elements in a slice, their complexity is somewhat different. In situations where performance requirements are high, we may need to choose a more efficient method, and when concise code is required, we can use an easier-to-understand method.

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