优化PHP数组数据在HTML表格中的分组显示：多地点记录合并技巧

$arr =
   [
      [
         'user_id' => 5,
         'l_id' => 10,
         'Name' => 'John Doe',
         'Location' => 'Chicago',
         'date' => '2021-10-02'
      ],
      [
         'user_id' => 5,
         'l_id' => 11,
         'Name' => 'John Doe',
         'Location' => 'Houston',
         'date' => '2021-10-02'
      ],
      [
         'user_id' => 6,
         'l_id' => 12,
         'Name' => 'Rob Doe',
         'Location' => 'Dallas',
         'date' => '2021-10-02'
      ],
      [
         'user_id' => 6,
         'l_id' => 13,
         'Name' => 'Rob Doe',
         'Location' => 'Philadelphia',
         'date' => '2021-10-02'
      ],
   ];

Name        Date          Location
John Doe    2021-10-02    Chicago
John Doe    2021-10-02    Houston
Rob Doe     2021-10-02    Dallas
Rob Doe     2021-10-02    Philadelphia

<?php

function arrayChanger($oldArray)
{
    $newArray = array();
    foreach ($oldArray as $item) {
        // 使用 user_id 作为主键对数据进行分组
        if (!isset($newArray[$item['user_id']])) {
            $newArray[$item['user_id']] = array(
                'user_id' => $item['user_id'],
                'Name' => $item['Name'],
                'date' => $item['date'],
                'UserLocations' => array() // 用于存储该用户的所有地点信息
            );
        }
        // 将地点信息添加到对应用户的 UserLocations 数组中
        $newArray[$item['user_id']]['UserLocations'][] = array(
            'Location' => $item['Location'],
            // 如果需要，也可以保留 l_id 或其他地点相关信息
            // 'l_id' => $item['l_id'],
        );
    }
    return $newArray;
}

// 示例调用
$groupedData = arrayChanger($arr);

/*
转换后的 $groupedData 结构大致如下：
[
    5 => [
        'user_id' => 5,
        'Name' => 'John Doe',
        'date' => '2021-10-02',
        'UserLocations' => [
            ['Location' => 'Chicago'],
            ['Location' => 'Houston']
        ]
    ],
    6 => [
        'user_id' => 6,
        'Name' => 'Rob Doe',
        'date' => '2021-10-02',
        'UserLocations' => [
            ['Location' => 'Dallas'],
            ['Location' => 'Philadelphia']
        ]
    ]
]
*/
?>

<?php
$htmlOutput1 = '<table>
    <thead>
        <tr>
            <th>Name</th>
            <th>Date</th>
            <th>Location</th>
        </tr>
    </thead>
<tbody>';

foreach ($groupedData as $userData) {
    $htmlOutput1 .= '<tr>
        <td>' . htmlspecialchars($userData['Name']) . '</td>
        <td>' . htmlspecialchars($userData['date']) . '</td>
        <td>';
        // 遍历该用户的所有地点，并用 <br> 分隔
        foreach ($userData['UserLocations'] as $locationData) {
            $htmlOutput1 .= htmlspecialchars($locationData['Location']) . "<br>";
        }
    $htmlOutput1 .= '</td>
        </tr>';
}

$htmlOutput1 .= '</tbody>
</table>';

echo $htmlOutput1;
?>

<table>
    <thead>
        <tr>
            <th>Name</th>
            <th>Date</th>
            <th>Location</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>John Doe</td>
            <td>2021-10-02</td>
            <td>Chicago<br>Houston<br></td>
        </tr>
        <tr>
            <td>Rob Doe</td>
            <td>2021-10-02</td>
            <td>Dallas<br>Philadelphia<br></td>
        </tr>
    </tbody>
</table>

<?php
$htmlOutput2 = '<table>
    <thead>
        <tr>
            <th>Name</th>
            <th>Date</th>
            <th>Location</th>
        </tr>
    </thead>
<tbody>';

foreach ($groupedData as $userData) {
    $isFirstLocation = true; // 标志位，用于判断是否是该用户的第一个地点
    foreach ($userData['UserLocations'] as $locationData) {
        $htmlOutput2 .= '<tr>';
        if ($isFirstLocation) {
            // 第一个地点行显示姓名和日期
            $htmlOutput2 .= '<td>' . htmlspecialchars($userData['Name']) . '</td>';
            $htmlOutput2 .= '<td>' . htmlspecialchars($userData['date']) . '</td>';
            $isFirstLocation = false; // 标记为非第一个地点
        } else {
            // 后续地点行将姓名和日期单元格留空
            $htmlOutput2 .= '<td></td>';
            $htmlOutput2 .= '<td></td>';
        }
        $htmlOutput2 .= '<td>' . htmlspecialchars($locationData['Location']) . '</td>';
        $htmlOutput2 .= '</tr>';
    }
}

$htmlOutput2 .= '</tbody>
</table>';

echo $htmlOutput2;
?>

<table>
    <thead>
        <tr>
            <th>Name</th>
            <th>Date</th>
            <th>Location</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>John Doe</td>
            <td>2021-10-02</td>
            <td>Chicago</td>
        </tr>
        <tr>
            <td></td>
            <td></td>
            <td>Houston</td>
        </tr>
        <tr>
            <td>Rob Doe</td>
            <td>2021-10-02</td>
            <td>Dallas</td>
        </tr>
        <tr>
            <td></td>
            <td></td>
            <td>Philadelphia</td>
        </tr>
    </tbody>
</table>