Lua table(表)
Lua table(表)
Lua table 是 Lua 的一种数据结构用来帮助我们创建不同的数据类型,如:数字、字典等。
Lua table 使用关联型数组,你可以用任意类型的值来作数组的索引,但这个值不能是 nil。
Lua table 是不固定大小的,你可以根据自己需要进行扩容。
Lua也是通过table来解决模块(module)、包(package)和对象(Object)的。 例如string.format表示使用"format"来索引table string。
table(表)的构造
构造器是创建和初始化表的表达式。表是Lua特有的功能强大的东西。最简单的构造函数是{},用来创建一个空表。可以直接初始化数组:
--sample table initialization mytable = {} --simple table value assignment mytable[1]= "Lua" --removing reference mytable = nil -- lua garbage collection will take care of releasing memory
当我们为 table a 并设置元素,然后将 a 赋值给 b,则 a 与 b 都指向同一个内存。如果 a 设置为 nil ,则 b 同样能访问 table 的元素。如果没有指定的变量指向a,Lua的垃圾回收机制会清理相对应的内存。
以下实例演示了以上的描述情况:
-- Simple empty table mytable = {} print("Type of mytable is ",type(mytable)) mytable[1]= "Lua" mytable["wow"] = "Tutorial" print("mytable Element at index 1 is ", mytable[1]) print("mytable Element at index wow is ", mytable["wow"]) -- alternatetable and mytable refers to same table alternatetable = mytable print("alternatetable Element at index 1 is ", alternatetable[1]) print("mytable Element at index wow is ", alternatetable["wow"]) alternatetable["wow"] = "I changed it" print("mytable Element at index wow is ", mytable["wow"]) -- only variable released and and not table alternatetable = nil print("alternatetable is ", alternatetable) -- mytable is still accessible print("mytable Element at index wow is ", mytable["wow"]) mytable = nil print("mytable is ", mytable)
以上代码执行结果为:
Type of mytable is table mytable Element at index 1 is Lua mytable Element at index wow is Tutorial alternatetable Element at index 1 is Lua mytable Element at index wow is Tutorial mytable Element at index wow is I changed it alternatetable is nil mytable Element at index wow is I changed it mytable is nil
Table 操作
以下列出了 Table 操作常用的方法
table.concat (table [, sep [, start [, end]]]):根据给定的参数在表中设置字符串。详见示例。
table.insert (table, [pos,] value):在指定位置将值插入表中。
table.maxn (table):返回最大的数值索引。
table.remove (table [, pos]):从表中删除值。
table.sort (table [, comp]):用指定的比较参数对table进行排序。
接下来我们来看下这几个方法的实例。
Table 连接
我们可以使用 concat() 方法来连接两个 table:
fruits = {"banana","orange","apple"} -- returns concatenated string of table print("Concatenated string ",table.concat(fruits)) --concatenate with a character print("Concatenated string ",table.concat(fruits,", ")) --concatenate fruits based on index print("Concatenated string ",table.concat(fruits,", ", 2,3))
执行以上代码输出结果为:
Concatenated string bananaorangeapple Concatenated string banana, orange, apple Concatenated string orange, apple
插入和移除
以下实例演示了 table 的插入和移除操作:
fruits = {"banana","orange","apple"} -- insert a fruit at the end table.insert(fruits,"mango") print("Fruit at index 4 is ",fruits[4]) --insert fruit at index 2 table.insert(fruits,2,"grapes") print("Fruit at index 2 is ",fruits[2]) print("The maximum elements in table is",table.maxn(fruits)) print("The last element is",fruits[5]) table.remove(fruits) print("The previous last element is",fruits[5])
执行以上代码输出结果为:
Fruit at index 4 is mango Fruit at index 2 is grapes The maximum elements in table is 5 The last element is mango The previous last element is nil
Table 排序
以下实例演示了 sort() 方法的使用,用于对 Table 进行排序:
fruits = {"banana","orange","apple","grapes"} for k,v in ipairs(fruits) do print(k,v) end table.sort(fruits) print("sorted table") for k,v in ipairs(fruits) do print(k,v) end
执行以上代码输出结果为:
1 banana 2 orange 3 apple 4 grapes sorted table 1 apple 2 banana 3 grapes 4 orange