如何迭代嵌套数组？

Question

我需要将以下数组结构打印为：

Node Title 1

  topic 1

  topic 2

  topic 3

  topic 4

    asset title1 

    asset title2

    asset title3

我如何使用 foreach - PHP

我所做的是：

foreach($output['fields'] as $key => $value) {
        if($key == 'title') {
            echo $value;
        }
        if(count($value['main_topic'])) {
            foreach($value['main_topic'] AS $mainkey => $main_topic) {
                echo $main_topic['topic_title'];
            }
        }
    }

上面的语法是打印标题。但不是 main_topic 数组。

Array
(
    [fields] => Array
        (
            [nid] => 136
            [node_title] => Node title 1
            [node_type] => curriculum
            [title] => Node title 1
            [main_topic] => Array
                (
                    [0] => Array
                        (
                            [row_id] => 136
                            [topic_id] => 411847
                            [weight] => 10
                            [topic_title] => topic 1
                        )

                    [1] => Array
                        (
                            [row_id] => 136
                            [topic_id] => 411839
                            [weight] => 2
                            [topic_title] => topic 2
                        )

                    [2] => Array
                        (
                            [row_id] => 136
                            [topic_id] => 411840
                            [weight] => 3
                            [topic_title] => topic 3
                        )

                    [3] => Array
                        (
                            [row_id] => 136
                            [topic_id] => 411841
                            [weight] => 4
                            [topic_title] => topic 4
                            [subfield] => Array
                                (
                                    [1] => Array
                                        (
                                            [asset_title] => asset title 1
                                        )

                                    [2] => Array
                                        (
                                            [asset_title] => asset title 2
                                        )

                                    [3] => Array
                                        (
                                            [asset_title] => asset title 3
                                        )

                                )

                        )


                )

        )

)

Answer 1

那是因为你正在迭代所有

$output['fields']

。 永远不会有带有键

$value

的

'main_topic'

，因为键

'main_topic'

包含在

$output['fields']

数组中，因此在 foreach 中仅作为

$key

存在。你想要的数组是

$value

你的代码应该是这样的：

foreach($output['fields'] as $key => $value) {
        if($key == 'title') {
            echo $value;
            continue;
        }
        if($key == 'main_topic' && is_array($value)) {
            foreach($value as $main_topic) {
                echo $main_topic['topic_title'];
            }
        }
    }

---

为了用完整的解决方案（包括资产标题）来完成这个答案，下面是我的编写方式。

因为

$output['fields']

是起点，为了使代码更具可读性，我使用

=&

运算符创建对起始节点的引用，这样数组就不会复制到内存中。我对内部

foreach

也做了同样的事情。由于我们不修改数据，引用变量就足够了，并且消耗更少的内存和 CPU:

if (is_array($output['fields'])) {
    $node =& $output['fields'];
    echo $node['title'];
    if(is_array($node['main_topic'])) {
        foreach($node['main_topic'] as &$main) {
            echo $main['topic_title'];
            if(is_array($main['subfield'])) {
                foreach($main['subfield'] as &$asset) {
                    echo $asset['asset_title'];
                }
            }
        }
    } 
}
else {
    echo "no menu";
}

Answer 2

$value

是数组，而不是

$key['main_topic']

foreach($output['fields'] as $key => $value) {
    if($key == 'title') {
        echo $value;
    }
    if($key == 'main_topic') {
        foreach($value as $mainkey => $main_topic) {
            echo $main_topic['topic_title'];
        }
    }
}

Answer 3

试试这个，你需要额外的密钥：

echo $value['main_topic'][$mainkey]['topic_title'];

Answer 4

您的数组部分感到困惑。

尝试（我还没有测试过）：

echo $output['node_title']."\n";
foreach ($output['fields'] as $key=>$value)
{
    switch ($key)
    {
        case 'title':
            echo $value."\n";
            break;
        case 'main_topic':
            if (count($value) > 0)
            {
                foreach ($value as $main_block)
                {
                    echo "\t".$main_block['topic_title']."\n";
                    if (array_key_exists('subfield',$main_block)!==FALSE)
                    {
                        foreach ($main_block['subfield'] as $subfield_block)
                        {
                            echo "\t\t".$subfield_block['asset_title']."\n";
                        }
                    }
                }
            }
            break;
        default:
            break;
    }
}