0xD34F

Вот говнокод:

$result = [];

foreach ($arr as $n) {
  for ($visited = []; array_key_exists($n, $arr); $visited[] = $n, $n = $arr[$n]) {
    if (($i = array_search($n, $visited)) !== false) {
      $loop = array_slice($visited, $i);
      if (empty(array_intersect(array_column($result, 0), $loop))) {
        $result[] = $loop;
      }
      break;
    }
  }
}

или

$result = [];
$visited = [];
$iLoop = -1;

foreach ($arr as $n) {
  for ($iLoop++; isset($arr[$n]); $visited[$n] = $iLoop, $n = $arr[$n]) {
    if (isset($visited[$n])) {
      if ($visited[$n] === $iLoop) {
        for ($loop = [ $m = $n ]; ($m = $arr[$m]) !== $n; $loop[] = $m) ;
        $result[] = $loop;
      }
      break;
    }
  }
}

$grouped = [];

foreach ($arr as [ 'id' => $id, 'name' => $name, 'key' => $key ]) {
  $grouped[$key][$name] ??= [ 'name' => $name, 'ids' => [] ];
  $grouped[$key][$name]['ids'][] = $id;
}

foreach ($keys as $k) {
  $$k = array_map(fn($n) => [
    'name' => $n['name'],
    'ids' => implode(', ', $n['ids'])
  ], array_values($grouped[$k] ?? []));
}

function getCombinations($arr, $keys = [], $vals = []) {
  return ($n = $arr[count($keys)] ?? null)
    ? array_merge(...array_map(
        fn($k) => getCombinations(
          $arr,
          [ ...$keys, $k ],
          [ ...$vals, ...$n[$k] ]
        ),
        array_keys($n)
      ))
    : [ implode('_', $keys) => $vals ];
}

function createTree($data, $params = []) {
  extract($params + [
    'levelKey' => 'level',
    'childrenKey' => 'children',
  ]);

  $root = [];

  foreach ($data as $n) {
    $arr = &$root;

    for (
      $level = $data[0][$levelKey];
      $level++ < $n[$levelKey];
      $arr = &$arr[count($arr) - 1][$childrenKey]
    ) ;

    $arr[] = $n + [ $childrenKey => [] ];
  }

  return $root;
}


$tree = createTree($arMenu, [ 'levelKey' => 'LEVEL' ]);

или

function createTree($data, $params = []) {
  $levelKey = $params['levelKey'] ?? 'level';
  $childrenKey = $params['childrenKey'] ?? 'children';

  $root = [];
  $stack = [ [ $data[0][$levelKey], &$root ] ];

  foreach ($data as $n) {
    $end = end($stack);
    $level = $n[$levelKey];

    if ($level > $end[0]) {
      $stack[] = [ $level, &$end[1][count($end[1]) - 1][$childrenKey] ];
    } else while ($level < end($stack)[0]) {
      array_pop($stack);
    }

    end($stack)[1][] = array_merge($n, [ $childrenKey => [] ]);
  }

  return $root;
}

$extract = fn($keys, $item) => array_combine($keys, array_map(fn($k) => $item[$k], $keys));

$grouped = [];
$productKeys = [ 'product_id', 'sku', 'quantity' ];
$orderKeys = array_diff(array_keys($arr[0] ?? []), $productKeys);

foreach ($arr as $n) {
  $id = $n['order_id'];
  $grouped[$id] ??= $extract($orderKeys, $n);
  $grouped[$id]['products'][] = $extract($productKeys, $n);
}

function merge($arrs, $idKey, ...$sumKeys) {
  $result = [];

  foreach (array_merge(...$arrs) as $n) {
    $id = $n[$idKey];
    $result[$id] ??= array_merge($n, array_combine($sumKeys, array_fill(0, count($sumKeys), 0)));

    foreach ($sumKeys as $k) {
      $result[$id][$k] += $n[$k];
    }
  }

  return array_values($result);
}


$result = merge($dates1, 'date', 'qty');

function f(&$x) {
  $x = 666;
}

f($xxx);

echo $xxx; // 666

preg_replace('/([а-яё])([А-ЯЁ])/u', '$1. $2', $str)

или

implode('. ', preg_split('/(?<=[а-яё])(?=[А-ЯЁ])/u', $str))

$arr2 = array_combine(array_column($arr, 'sku'), $arr);
$result = array_map(fn($n) => $arr2[$n], $torgPred);

или

$result = array_filter($arr, fn($n) => in_array($n['sku'], $torgPred));

$value = array_combine($data['value_index'], $data['value'])[min($data['value_index'])];

или

$value = $data['value'][array_search(min($data['value_index']), $data['value_index'])];

или

$index = 0;

for ($i = 1; $i < count($data['value_index']); $i++) {
  if ($data['value_index'][$i] < $data['value_index'][$index]) {
    $index = $i;
  }
}

$value = $data['value'][$index];

$values = array_column($array2, 'value');
$result = array_filter($array1, fn($n) => in_array($n->code, $values));

function getUrls($tree, $url = '') {
  $urls = [];

  foreach ($tree as $n) {
    $newUrl = ($url ? $url.'/' : '').$n->url;
    array_push($urls, $newUrl, ...getUrls($n->subcategories ?? [], $newUrl));
  }

  return $urls;
}

$toStr = fn($arr) => implode('', array_map(fn($k) => "[$k:]$arr[$k][:$k]", array_keys($arr)));
print_r(array_map($toStr, $lang));

почему ошибку выдает?

Потому что вы условие задачи до конца не прочитали. Или прочитали, но не поняли. Что должна делать ваша функция:

It should take an array of numbers as its argument and return the two highest numbers within the array.

Что означает "return" знаете? Никакого foreach-echo не надо:

function twoOldestAges($ages) {
  sort($ages);
  return array_slice($ages, -2);
}

А вообще, от вас при решении этой задачи другого ждут, сложность должна быть линейной:

function twoOldestAges($ages) {
  $a = -INF;
  $b = -INF;

  foreach ($ages as $n) {
    if ($n > $a) {
      $b = $a;
      $a = $n;
    } else if ($n > $b) {
      $b = $n;
    }
  }
  
  return [ $b, $a ];
}

Собрать новый массив:

$newArr = array_filter($arr, fn($n) => explode('.', $n)[1] !== '08');

Изменить существующий:

for ($i = 0, $j = 0; $i < count($arr); $i++) {
  if (explode('.', $arr[$i])[1] === '08') {
    $j++;
  } else if ($j) {
    $arr[$i - $j] = $arr[$i];
  }
}

array_splice($arr, -$j, $j);

^\d{8}(\d{4})?$

^(?!.*__)@[a-z][a-z\d_]{4,34}$

$minPrices = array_values(array_reduce($arr, function($acc, $n) {
  $key = $n['code_id'];
  if (!isset($acc[$key]) || $acc[$key]['price'] > $n['price']) {
    $acc[$key] = $n;
  }

  return $acc;
}, []));