基于Laravel集合/数组更新首个集合/数组的值，若不存在则置为0

本文旨在解决在Laravel中，如何基于第二个集合/数组的值来更新第一个集合/数组的值，并且当第二个集合/数组中不存在对应项时，将第一个集合/数组中的值置为0的问题。我们将提供一种高效且简洁的方法，通过引用和查找表来实现这一目标，避免使用复杂的集合操作。

解决方案

该方案的核心思想是：首先遍历第一个数组，将其 points 值初始化为 0，并建立一个 name 到 points 的引用查找表。然后，遍历第二个数组，利用查找表将第二个数组中的 points 值更新到第一个数组中对应的 points 引用。

以下是具体实现步骤和代码示例：

1. 准备数据

   假设我们有两个数组 $first 和 $second，结构如下：

   $first = [
       "name" => "Test A",
       "scores" => [
           ["name" => "Values", "points" => 9],
           ["name" => "Algebra", "points" => 6],
           ["name" => "Science", "points" => 5],
           ["name" => "Total", "points" => 20]
       ]
   ];
   
   $second = [
       "name" => "Test A",
       "scores" => [
           ["name" => "Values", "points" => 5],
           ["name" => "Algebra", "points" => 8],
           ["name" => "Total", "points" => 13]
       ]
   ];

2. 初始化并创建查找表

   遍历 $first['scores']，将每个元素的 points 初始化为 0，并创建一个 $refPoints 数组，用于存储 name 到 points 的引用。

   foreach ($first['scores'] as ['name' => $name, 'points' => &$points]) {
       $points = 0;
       $refPoints[$name] =& $points;
   }

   注意： & 符号表示引用。$refPoints[$name] =& $points; 创建了一个 $refPoints[$name] 到 $points 的引用。这意味着，修改 $refPoints[$name] 的值，也会同时修改 $points 的值。

3. 更新 points 值

   遍历 $second['scores']，使用 $refPoints 查找表更新 $first['scores'] 中对应的 points 值。

   foreach ($second['scores'] as ['name' => $name, 'points' => $refPoints[$name]]);

   由于 $refPoints[$name] 是 $points 的引用，所以这一步直接修改了 $first['scores'] 中的 points 值。

4. 查看结果

   执行完以上步骤后，$first 数组将被更新为期望的结果：

   var_export($first);

   输出：

   array (
     'name' => 'Test A',
     'scores' => 
     array (
       0 => 
       array (
         'name' => 'Values',
         'points' => 5,
       ),
       1 => 
       array (
         'name' => 'Algebra',
         'points' => 8,
       ),
       2 => 
       array (
         'name' => 'Science',
         'points' => 0,
       ),
       3 => 
       array (
         'name' => 'Total',
         'points' => 13,
       ),
     ),
   )

完整代码示例

 "Test A",
    "scores" => [
        ["name" => "Values", "points" => 9],
        ["name" => "Algebra", "points" => 6],
        ["name" => "Science", "points" => 5],
        ["name" => "Total", "points" => 20]
    ]
];

$second = [
    "name" => "Test A",
    "scores" => [
        ["name" => "Values", "points" => 5],
        ["name" => "Algebra", "points" => 8],
        ["name" => "Total", "points" => 13]
    ]
];

foreach ($first['scores'] as ['name' => $name, 'points' => &$points]) {
    $points = 0;
    $refPoints[$name] =& $points;
}

foreach ($second['scores'] as ['name' => $name, 'points' => $refPoints[$name]]);

var_export($first);
?>

总结

该方法利用引用和查找表，避免了复杂的集合操作，提高了效率。适用于需要基于第二个集合/数组更新第一个集合/数组，并且当第二个集合/数组中不存在对应项时，需要将第一个集合/数组中的值置为默认值（例如 0）的场景。