Lua 中数组的奇怪行为

我是Lua的新手。我有两个数组

第一个:

levels={
-- 1
{
{9,9,9,9,9,9,9,9,9},
{9,9,9,9,9,9,9,9,9},
{9,9,1,0,9,0,3,9,9},
{9,9,9,9,9,9,9,9,9},
{9,9,9,9,9,9,9,9,9}
}
,
-- 2
{
{9,9,9,9,9},
{9,9,9,9,9},
{9,9,1,9,9},
{9,9,0,9,9},
{9,9,0,9,9},
{9,9,0,9,9},
{9,9,0,9,9},
{9,9,3,9,9},
{9,9,9,9,9},
{9,9,9,9,9}
}
,
-- 3
{
{9,9,9,9,9,9,9,9,9,9},
{9,9,9,9,9,9,9,9,9,9},
{9,9,0,9,0,9,9,9,9,9},
{9,9,1,0,0,9,0,3,9,9},
{9,9,9,9,9,9,9,9,9,9},
{9,9,9,9,9,9,9,9,9,9}
}
}

而第二个数组我是这样声明的:

playingLevel=levels [1]

问题是，当我改变playingLevel的值之后，levels数组也以同样的方式发生改变。我想只更改playingLevel。