另一种方法是利用Larvel的集合获取副本，并将它们传递到视图中。

$ips = $promos->participants->pluck('ip');
$duplicateIps = $ips->duplicates()->unique()->all();

所以在你的刀片里你只需要检查

@if($promos->participants->isNotEmpty())
@foreach($promos->participants as $participant)
<table>
  <tr class="align-middle">
    <td>Name</td>
    <td>Email</td>
    <td>Username</td>
    <td>IP</td>
  </tr>
  <tr @class(['duplicate-row' => in_array($participant->ip, $duplicateIps)]>
    <td>{{$participant->name}}</td>
    <td>{{$participant->email}}</td>
    <td>{{$participant->username}}</td>
    <td>{{$participant->ip}}</td>
  </tr>
</table>
@endforeach

像这样做
$ipList将在foreach运行时存储IP，并不断检查它们是否存在。如果存在，则将类duplicate-row添加到<tr>

$ipList = [];
@foreach($promos->participants as $participant)
  <tr class="align-middle @if(in_array($participant->ip, $ipList)) duplicate-row @endif">
    <td>{{$participant->name}}</td>
    <td>{{$participant->email}}</td>
    <td>{{$participant->username}}</td>
    <td>{{$participant->ip}}</td>
  </tr>
  @if(!in_array($participant->ip, $ipList))
    <?php array_push($ipList, $participant->ip); ?>
  @endif
@endforeach

在CSS中，您可以添加

.duplicate-row {
  background-color: red;
}