php get duplicate data once in array object

You can have a nested loop to get the data that you want. Here is what I did:

<?php
// Create array of objects
$fields = array
    (
     "filed_p_1" => (object) [
        "field_id" => 1,
        "field_table" => "product",
        "field_realname" => "field one",
        "field_namekey" => "filed_p_1",
        "field_header" => "number_one",
        "field_type" => "text"
    ],

"filed_p_2" => (object) [
        "field_id" => 2,
        "field_table" => "product",
        "field_realname" => "field two",
        "field_namekey" => "filed_p_2",
        "field_header" => "number_two",
        "field_type" => "text"
    ],

"filed_p_3" => (object) [
        "field_id" => 3,
        "field_table" => "product",
        "field_realname" => "field three",
        "field_namekey" => "filed_p_3",
        "field_header" => "number_three",
        "field_type" => "text"

    ],

"filed_p_1_2" => (object) [
        "field_id" => 19,
        "field_table" => "product",
        "field_realname" => "field four",
        "field_namekey" => "filed_p_1_2",
        "field_header" => "number_one",
        "field_type" => "text"
    ]

  );

  // Create array for headers
  $header_array = array();

  // Loop through each array object
  foreach ($fields as $key => $value) {
    // Set header value
    $header = $value->field_header;
    // Check if header value has already been used, proceed if not
    if(!in_array($header,$header_array)) {
      // Add header value to $header_array and echo header
      $header_array[] = $header;
      echo $header;
      echo "<br />";
      // Loop through $fields again and echo every field_realname with that header
      foreach ($fields as $fieldName => $oneExtraField) {
        if($header == $oneExtraField->field_header) {
          echo $oneExtraField->field_realname;
          echo "<br />";
        }
      }
      echo "<br />";
    }
  }
?>

This outputs:

number_one
field one
field four

number_two
field two

number_three
field three