Lua table (table)

Lua table (table)

Table is a data structure used by Lua to help us create different data types, such as numbers, dictionaries, and so on.

Lua table uses an array of associations, which you can index with any type of value, but this value cannot be nil.

Lua table is not a fixed size and you can expand it to your needs.

Lua also solves modules, packages, and objects through table. For example, string.format indicates the use of "format" to index the table string.

The construction of the table

A constructor is an expression that creates and initializes a table. T ables are something unique and powerful to Lua. T he simplest constructor is , which is used to create an empty table. The array can be initialized directly:

-- 初始化表
mytable = {}

-- 指定值
mytable[1]= "Lua"

-- 移除引用
mytable = nil
-- lua 垃圾回收会释放内存

When we set the element for table a and then assign a to b, a and b both point to the same memory. I f a is set to nil, b also has access to the table element. If no specified variable points to a, Lua's garbage collection mechanism cleans up the corresponding memory.

The following example demonstrates the above description:

-- 简单的 table
mytable = {}
print("mytable 的类型是 ",type(mytable))

mytable[1]= "Lua"
mytable["wow"] = "修改前"
print("mytable 索引为 1 的元素是 ", mytable[1])
print("mytable 索引为 wow 的元素是 ", mytable["wow"])

-- alternatetable和mytable的是指同一个 table
alternatetable = mytable

print("alternatetable 索引为 1 的元素是 ", alternatetable[1])
print("mytable 索引为 wow 的元素是 ", alternatetable["wow"])

alternatetable["wow"] = "修改后"

print("mytable 索引为 wow 的元素是 ", mytable["wow"])

-- 释放变量
alternatetable = nil
print("alternatetable 是 ", alternatetable)

-- mytable 仍然可以访问
print("mytable 索引为 wow 的元素是 ", mytable["wow"])

mytable = nil
print("mytable 是 ", mytable)

The above code execution results are:

mytable 的类型是 	table
mytable 索引为 1 的元素是 	Lua
mytable 索引为 wow 的元素是 	修改前
alternatetable 索引为 1 的元素是 	Lua
mytable 索引为 wow 的元素是 	修改前
mytable 索引为 wow 的元素是 	修改后
alternatetable 是 	nil
mytable 索引为 wow 的元素是 	修改后
mytable 是 	nil

Table action

Here's a list of common ways table operations:

Let's look at some examples of these methods.

Table connection

We can use the concat() method to connect two table:

fruits = {"banana","orange","apple"}
-- 返回 table 连接后的字符串
print("连接后的字符串 ",table.concat(fruits))

-- 指定连接字符
print("连接后的字符串 ",table.concat(fruits,", "))

-- 指定索引来连接 table
print("连接后的字符串 ",table.concat(fruits,", ", 2,3))

The above code output results in:

连接后的字符串 	bananaorangeapple
连接后的字符串 	banana, orange, apple
连接后的字符串 	orange, apple

Insert and remove

The following example demonstrates the insertion and removal of table:

fruits = {"banana","orange","apple"}

-- 在末尾插入
table.insert(fruits,"mango")
print("索引为 4 的元素为 ",fruits[4])

-- 在索引为 2 的键处插入
table.insert(fruits,2,"grapes")
print("索引为 2 的元素为 ",fruits[2])

print("最后一个元素为 ",fruits[5])
table.remove(fruits)
print("移除后最后一个元素为 ",fruits[5])

The above code output results in:

索引为 4 的元素为  mango
索引为 2 的元素为   grapes
最后一个元素为     mango
移除后最后一个元素为   nil

Table sorting

The following example demonstrates the use of the sort() method for sorting Table:

fruits = {"banana","orange","apple","grapes"}
print("排序前")
for k,v in ipairs(fruits) do
  print(k,v)
end

table.sort(fruits)
print("排序后")
for k,v in ipairs(fruits) do
   print(k,v)
end

The above code output results in:

排序前
1   banana
2   orange
3   apple
4    grapes
排序后
1  apple
2    banana
3   grapes
4   orange

Table maximum

Table.maxn After Lua5.2, the method no longer exists, and we define the table_maxn method implementation.

The following example shows how to get the maximum value in table:

function table_maxn(t)
    local mn = 0
    for k, v in pairs(t) do
        if mn < k then
            mn = k
        end
    end
    return mn
end
tbl = {[1] = "a", [2] = "b", [3] = "c", [26] = "z"}
print("tbl 长度 ", #tbl)
print("tbl 最大值 ", table_maxn(tbl))

The above code output results in:

tbl 长度    3
tbl 最大值  26