I need an array in which the values (dates) are not repeated, the array is generated from a select loop

while ($linha = $pdo->fetch(PDO::FETCH_ASSOC)) {

if($linha['previsto_pasta'] == 0){

} else{


echo "<tr>";
echo  "<td><div class='previsto'>{$linha['previsto']}</div></td>";    
echo  "<td><div class='quantitativo'>{$linha['quantitativo']}</div></td>";    
echo  "<td><div class='qualitativo'>{$linha['qualitativo']}</div></td>"; 

$linha = $newArray[] = array(
        $linha['p_data'], 
        $linha['p_data_t'], 
        $linha['p_data_f'], 
    );
    $result =  array_unique($newArray);


    /* echo  "<td><div class='pi_p_data'>{$linha['']}</div></td>";  */

echo "</tr>";   

    }
}

It gives the following error: Notice: Array to string conversion