How to copy an object into another object with generated keys?

I' am trying to scrape a specific webpage and its sub-pages for later use within an web application.

Unfortunally I 'am failing to copy my history object created by the getHistory()-Method into my umfragen object.

 $history = $this->getHistory($j, $i);
 //$history = (object) [];
 $td = $this->getData($tr, $inst, $date, $party, $j, $history);
 $this->umfragen->{$party}->{$inst} = $td;

My object keys are generated on the fly. If i call the $this->getHistory() on its own and echo its result everything works fine.

Can somebody pls explain me what I'am doing wrong?

Many thanks!

<?php
require('vendor/autoload.php');

header('Content-type: application/xml');
header("Access-Control-Allow-Origin: *");


use PHPHtmlParser\Dom;



ini_set('max_execution_time', 300); //300 seconds = 5 minutes


class Scrpr {

private $institutes = array("allensbach", "emnid", "forsa", "politbarometer", "gms", "dimap", "insa");
private $parties = array("cdu/csu", "spd", "grüne", "fdp", "linke", "afd", "sonstige", "nw_un", "fw");
private $partyids = array("cdu", "spd", "gru", "fdp", "lin", "afd", "son");
private $theaders = array("CDU/CSU", "SPD", "GRÜNE", "FDP", "LINKE", "AfD", "Sonstige", "Nichtwähler/Unentschl.", "FW", "Befragte", "Zeitraum");

private $dom;
private $dates;
private $umfragen;

public function __construct() {
    $this->var2 = date("Y/m/d");
    $this->dom = new Dom;
    $this->dom->load('http://ift.tt/1d7VYiB');
    $this->dates = $this->getDomDates();
    $this->umfragen = (object) [];
}

public function toJson() {
    return json_encode($this->umfragen);
}

public function writeToJson() {
    $fp = fopen('results.json', 'w');
    fwrite($fp, json_encode($this->umfragen));
    fclose($fp);
}

public function run_history() {
    for ($i = 0; $i < sizeof($this->partyids); $i++) {
        $party = $this->partyids[$i];
        for ($j = 0; $j < sizeof($this->institutes); $j++) {
            $history = $this->getHistory($j, $i);


            $this->umfragen[$i][$j]->history = $history;

            //$this->umfragen->{$party}->{$inst}->history = new stdClass();
            //$this->umfragen->{$party}->{$inst}->history = $history;
        }
    }

  //return json_encode($history);
}

function getHistory($instId, $partyId) {

 $instName = $this->institutes[$instId];
 $partyName = $this->partyids[$partyId];

 $subDom = $this->dom;
 $html = $subDom->load('http://ift.tt/1d7VYiB'.$instName.".htm");
 $tbody = $html->find('tbody');

 $td_arr = [];

  if ($tbody) {
    $parent_splitted = $this->splitHtml($tbody);
    if ($parent_splitted != false) {
      for ($i = 0; $i < sizeof($parent_splitted); $i++) {
        $val = $parent_splitted[$i];
        if ($this->isEmpty($val)) {
          $date = "";
          if(preg_match("/\d{2}\.\d{2}.\d{4}/", $val, $matches)) {
            $date =  $matches[0];
          }
          else if (preg_match('#\d+(?:\,+\d{1})?#', $val, $matches) && strpos($val, '%')) {
              $td = (object) [
                "datum" => $date,
                "y" => $val,
              ];
              array_push($td_arr, $td);
          }
        }
      }
    }
  }

 $td_filtered = [];

for ($j = 0; $j < sizeof($td_arr); $j++) {
    if (fmod($j, 7) == $partyId) {
      array_push($td_filtered, $td_arr[$j]);
    }
}
  return $td_filtered;

}


public function run() {

    for ($i = 0; $i < sizeof($this->partyids); $i++) {
        $party = $this->partyids[$i];
        for ($j = 0; $j < sizeof($this->institutes); $j++) {
            $inst = $this->institutes[$j];
            $date = $this->dates[$j];
            $tr = $this->dom->find('tbody/tr[id='.$party.']');
            $history = $this->getHistory($j, $i);
            //$history = (object) [];
            $td = $this->getData($tr, $inst, $date, $party, $j, $history);
            $this->umfragen->{$party}->{$inst} = $td;
        }
    }
}

private function getData ($parent, $inst, $date, $party, $index , $history) {
  $td = (object) [];
  $result = [];
  $parent_splitted = $this->splitHtml($parent);

  if ($parent_splitted != false) {
    $td_arr = [];

    for ($i = 0; $i < sizeof($parent_splitted); $i++) {
        $val = $parent_splitted[$i];
        if ($this->isEmpty($val)) {
            if ($this->isNumValueEmpty($val)) {
                array_push($td_arr, $val);
            }
        }
      }
    }

    for ($j = 0; $j< sizeof($td_arr); $j++) {
        $val = $td_arr[$j];
        if ($j === $index) {
          $fval = str_replace(",", ".", $val);
          $td = (object) [
            "history" => $this->getHistory(1, 1),
            "datum" => $date,
            "y" => $fval,
          ];
        }
    }
  return $td;
}

private function getDomDates() {
    $html =  $this->dom->find('tbody/tr[id="datum"]')->innerHtml;
    $result = [];
    $dates_splitted = $this->splitHtml($html);
    foreach ($dates_splitted as $key => $value) {
        if ($this->isDate($value)) {
            $d = str_replace(".", "-", $value);
            $date=date_create($d);
            array_push($result, $date);
        }
    }
    return $result;
}

private function splitHtml($html) {
    //return preg_split('/<[^>]*[^\/]>/i', $html, -1, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE);
    return preg_split('/<[^>]*[^\/]>/i', $html, -1, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE);
}

private function isEmpty($val) {
  return preg_match('/\S/', $val);
}

private function isNumValueEmpty($val) {
  return preg_match('#\d+(?:\,\d{1,2})?#', $val);
}
private function isDate($val) {
  return preg_match("/\d{2}\.\d{2}.\d{4}/", $val);
}

private function getArrPosByVal($arr, $value) {
  $res = 0;
  for ($i = 0; $i < sizeof($arr); $i++) {
    if ($arr[$i] === $value) {
      $res = $i;
    }
  }
  return $res;
}
}

$scrpr = new Scrpr();

$scrpr->run();
//$scrpr->run_history();
//$scrpr->writeToJson();
echo ($scrpr->toJson());

?>