从子数组（PHP）中将数据推送到父数组答案

【问题标题】：Push data to a parent array from within child array (PHP)从子数组（PHP）中将数据推送到父数组
【发布时间】：2020-05-17 19:19:36
【问题描述】：

我有一系列棒球队，每个棒球队都有一系列球队的赛季。每个赛季内是该赛季的获胜次数。我想统计一个团队的所有胜利，然后将这个数字推送到每个团队的数据中。我的最终目标是按照每支球队的总胜场数对这个主数组进行排序。

我的问题是，我不知道如何将 totalGamesWon 计数推到团队数据的主数组中。

对于效率低下的编码提前道歉！如果像我这样的新手有更好的方法来做到这一点，我会全力以赴！

$teams = array(
  array (
    'teamName' => 'Yankees',
    'seasons' => array (
      array(
        'seasonName' => '2018 Regular Season',
        'wins' => 100
      ),
      array(
        'seasonName' => '2018 Playoffs',
        'wins' => 2
      )
    )
  ),
  array (
    'teamName' => 'Red Sox',
    'seasons' => array (
      array(
        'seasonName' => '2018 Regular Season',
        'wins' => 108
      ),
      array(
        'seasonName' => '2018 Playoffs',
        'wins' => 11
      )
    )
  ),
);

foreach ($teams as $team) {
  $totalGamesWon = 0;
  foreach ($team['seasons'] as $season) {
    $totalGamesWon += $season['wins'];
  }
  $team['totalGamesWon'] = $totalGamesWon;
}

echo $teams[0]['teamName'];       // outputs "Yankees"
echo $teams[0]['totalGamesWon'];  // should output "102". Instead, I get "Notice: Undefined index: totalGamesWon"

【问题讨论】：

这是问题吗？ foreach ($teams as &$team) {

标签： php mysql arrays

【解决方案1】：

只需将$team 更改为&$team，这样您就可以通过引用而不是按值传递$team：

foreach ($teams as &$team) {
   $totalGamesWon = 0;
   foreach ($team['seasons'] as $season) {
       $totalGamesWon += $season['wins'];
   }
   $team['totalGamesWon'] = $totalGamesWon;
}

默认情况下（$team）它是按值传递的，这意味着它只在范围内（在循环中）改变。因此每次迭代都会设置 $team['totalGameswon'] 的值，但实际数组 $teams 不受影响。

当它通过引用传递时，当前更改的项目 ($team['totalGamesWon']) 正在更改实际数组中的值。

所以： (按值传递)

foreach ($teams as $key => $team) {
   $totalGamesWon = 0;
   foreach ($team['seasons'] as $season) {
       $totalGamesWon += $season['wins'];
   }
   $teams[$key]['totalGamesWon'] = $totalGamesWon;
}

和（通过引用传递）

foreach ($teams as &$team) {
   $totalGamesWon = 0;
   foreach ($team['seasons'] as $season) {
       $totalGamesWon += $season['wins'];
   }
   $team['totalGamesWon'] = $totalGamesWon;
}

会给你同样的结果。

【讨论】：

【解决方案2】：

问题出在“foreach ($teams as $team)”

foreach() 创建一个新变量 $team，其中 $teams[] 的值在每个循环中都被复制。

这意味着 $team 是一个不同于 $teams[] 的变量。您将 totalGamesWon 写入 $team - 在下一个循环中被覆盖。 $teams[] 未受影响。

试试这个：

<?php

$teams = array(
    array (
      'teamName' => 'Yankees',
      'seasons' => array (
        array(
          'seasonName' => '2018 Regular Season',
          'wins' => 100
        ),
        array(
          'seasonName' => '2018 Playoffs',
          'wins' => 2
        )
      )
    ),
    array (
      'teamName' => 'Red Sox',
      'seasons' => array (
        array(
          'seasonName' => '2018 Regular Season',
          'wins' => 108
        ),
        array(
          'seasonName' => '2018 Playoffs',
          'wins' => 11
        )
      )
    ),
  );

  $teamsCount = count($teams) ;

  for ($i = 0; $i < $teamsCount; $i++ ) 
  {
    $totalGamesWon = 0;
    foreach ($teams[$i]['seasons'] as $season) {
      $totalGamesWon += $season['wins'];
    }
    $teams[$i]['totalGamesWon'] = $totalGamesWon;
  }

  echo $teams[0]['teamName'];       // outputs "Yankees"
  echo $teams[0]['totalGamesWon'];  // should output "102". Instead, I get "Notice: Undefined index: totalGamesWon"


die() ;
?>

【讨论】：

没有其他类型的 for 循环。您仍然可以使用包含密钥的 foreach-loop。