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Lua

Lua-表格

Lua-桌子


介绍

表是Lua中唯一可帮助我们创建数组和字典等不同类型的数据结构。 Lua使用关联数组,不仅可以用数字索引,还可以用字符串(除nil外)进行索引。桌子没有固定的大小,可以根据我们的需要增加。

Lua在所有表示形式(包括程序包表示形式)中使用表。当我们访问方法字符串.format时,这意味着我们正在访问字符串包中可用的格式函数。

表示法和用法

表称为对象,它们既不是值也不是变量。 Lua使用构造函数表达式{}创建一个空表。众所周知,持有表引用的变量与表本身之间没有固定的关系。

--sample table initialization
mytable = {}

--simple table value assignment
mytable[1]= "Lua"

--removing reference
mytable = nil

-- lua garbage collection will take care of releasing memory

当我们拥有一个包含元素集的表a并将表赋给b时ab都引用相同的内存。没有为b单独分配单独的内存。当a设置为nil时,b仍然可以访问表。当没有对表的引用时,Lua中的垃圾回收将负责清理过程,以使这些未引用的内存可以再次使用。

下面显示了一个示例,用于解释表的上述功能。

-- 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("alternatetable 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)

当我们运行上面的程序时,我们将获得以下输出-

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
alternatetable 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

表操作

内置了用于表操作的函数,这些函数在下表中列出。

Sr.No. Method & Purpose
1

table.concat (table [, sep [, i [, j]]])

Concatenates the strings in the tables based on the parameters given. See example for detail.

2

table.insert (table, [pos,] value)

Inserts a value into the table at specified position.

3

table.maxn (table)

Returns the largest numeric index.

4

table.remove (table [, pos])

Removes the value from the table.

5

table.sort (table [, comp])

Sorts the table based on optional comparator argument.

让我们看看上述功能的一些示例。

表串联

我们可以使用concat函数来连接两个表,如下所示-

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))

当我们运行上面的程序时,我们将获得以下输出-

Concatenated string     bananaorangeapple
Concatenated string     banana, orange, apple
Concatenated string     orange, apple

插入和移除

在表操作中,表项的插入和删除是最常见的。下面说明。

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])

当我们运行上面的程序时,我们将获得以下输出-

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

排序表

我们经常需要按特定顺序对表格进行排序。排序功能按字母顺序对表中的元素进行排序。如下所示。

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

当我们运行上面的程序时,我们将获得以下输出-

1    banana
2    orange
3    apple
4    grapes
sorted table
1    apple
2    banana
3    grapes
4    orange
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