PHP проверка одинаковых значений в цикле

$result_string = "";
    foreach ($sequnce as $key => $value) {    
        $result_string .= $value['psevdonim'] . ", ";
    }
    $result_string = substr($result_string, 0, -2);

$sequnce=array(
    array("rang"=>"3","psevdonim"=>"Z1"),
    array("rang"=>"1","psevdonim"=>"Z2"),
    array("rang"=>"1","psevdonim"=>"Z3"),
    array("rang"=>"2","psevdonim"=>"Z4"),
);
 
$arnew=array();
 
foreach ($sequnce as $key => $value) {    
    $arnew[$value["rang"]][]=$value['psevdonim'];
}
$str="";
$k=0;
foreach($arnew as $key=>$value){
    if($k>0) $str.=", ";
    if (count($value)>1){
        $str.="(".implode(", ",$value).")";
    }else{
        $str.=$value[0];
    }
$k++;
}
echo $str;

$sequnce = array(
    0 => array('rang'=>1,'psevdonim'=>'Z1'),
    1 => array('rang'=>2,'psevdonim'=>'Z2'),
    2 => array('rang'=>3,'psevdonim'=>'Z3'),
    3 => array('rang'=>4,'psevdonim'=>'Z4'),
    4 => array('rang'=>3,'psevdonim'=>'Z5'),
    5 => array('rang'=>3,'psevdonim'=>'Z6')
);
$result_string = "";
$i = 0;
foreach ($sequnce as $key=>$item) {
    if (strpos($result_string,$item['psevdonim']) !== false) continue;
    if ($i++ > 0) $result_string .= ", ";
    $concat_by_rang = $item['psevdonim'];
    foreach ($sequnce as $key2=>$item2) {
        if (($item['rang'] == $item2['rang']) && ($item['psevdonim'] != $item2['psevdonim']))
        {
            $concat_by_rang .= " - ".$item2['psevdonim'];
        }
    }
    if (strpos($concat_by_rang,'-')) $concat_by_rang = "(".$concat_by_rang.")";
    $result_string .= $concat_by_rang;
}
 
echo $result_string;

$sequnce = array(
    array('rang' => 1, 'psevdonim' => 'Z1'),
    array('rang' => 2, 'psevdonim' => 'Z2'),
    array('rang' => 3, 'psevdonim' => 'Z3'),
    array('rang' => 4, 'psevdonim' => 'Z4'),
    array('rang' => 3, 'psevdonim' => 'Z5'),
    array('rang' => 3, 'psevdonim' => 'Z6')
);
 
array_multisort(array_map(function($row) {
    return $row['rang'];
}, $sequnce), SORT_ASC, $sequnce);
 
$arResult = array(); $arUseRang = array();
foreach($sequnce as $row) {
    if (!in_array($row['rang'], $arUseRang))
        $arUseRang[] = $row['rang'];
    else continue;
    $arFormat = array_map(function ($row) {
        return $row['psevdonim'];
    }, array_filter($sequnce, function($row) use ($arUseRang) {
        return $row['rang'] == end($arUseRang);
    }));
    $arResult[] = count($arFormat) > 1 ? '(' . implode("\040-\040", $arFormat) . ')' : array_shift($arFormat);
};
$strResult = implode(",\040", $arResult);
 
echo $strResult;