在php中不使用explode将字符串转换为数组

我想在mongoDB数据库中将字符串保存为数组。 我得到以下字符串，需要将其转换为数组，以便在mongoDB数据库中存储数据。
我使用的是codeigniter框架

输入字符串

"[ [ 18, 18, 18, 18, 18, 18, 18, 18, 18 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ] ]"

期望输出

[ 
    [ 
        18, 
        18, 
        18, 
        18, 
        18, 
        18, 
        18, 
        18, 
        18
    ], 
    [ 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2
    ], 
    [ 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2
    ], 
    [ 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2
    ], 
    [ 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2
    ], 
    [ 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2
    ], 
    [ 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2
    ], 
    [ 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2
    ], 
    [ 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2, 
        2
    ]

提前谢谢

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这看起来像JSON，那么为什么不使用JSON解析器呢

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这是一个字符串，所以它不起作用，我试试看

它确实是一个JSON字符串，与您的说法相反：）

---

这看起来像JSON，为什么不使用JSON解析器呢？它是一个字符串，所以不起作用，我试试看。@Ranpariya？！？！JSON是一种字符串格式。我只是在解析器中尝试了一下，效果很好。

<?php

print_r( json_decode("[ [ 18, 18, 18, 18, 18, 18, 18, 18, 18 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ], [ 2, 2, 2, 2, 2, 2, 2, 2, 2 ] ]"));

Array
(
    [0] => Array
        (
            [0] => 18
            [1] => 18
            [2] => 18
            [3] => 18
            [4] => 18
            [5] => 18
            [6] => 18
            [7] => 18
            [8] => 18
        )

    [1] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 2
            [3] => 2
            [4] => 2
            [5] => 2
            [6] => 2
            [7] => 2
            [8] => 2
        )

    [2] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 2
            [3] => 2
            [4] => 2
            [5] => 2
            [6] => 2
            [7] => 2
            [8] => 2
        )

    [3] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 2
            [3] => 2
            [4] => 2
            [5] => 2
            [6] => 2
            [7] => 2
            [8] => 2
        )

    [4] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 2
            [3] => 2
            [4] => 2
            [5] => 2
            [6] => 2
            [7] => 2
            [8] => 2
        )

    [5] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 2
            [3] => 2
            [4] => 2
            [5] => 2
            [6] => 2
            [7] => 2
            [8] => 2
        )

    [6] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 2
            [3] => 2
            [4] => 2
            [5] => 2
            [6] => 2
            [7] => 2
            [8] => 2
        )

    [7] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 2
            [3] => 2
            [4] => 2
            [5] => 2
            [6] => 2
            [7] => 2
            [8] => 2
        )

    [8] => Array
        (
            [0] => 2
            [1] => 2
            [2] => 2
            [3] => 2
            [4] => 2
            [5] => 2
            [6] => 2
            [7] => 2
            [8] => 2
        )

)