array_splice vs array_unshift

[ggalan]

i am trying to reorganize my json file using array_splice.
this is part of my code, using array_unshift works great, but i dont want the item placed on the end,
rather i would like to replace the original spot using splice but i get weird out put

$dataFile = 'data/data.json';
$dataTxt = file_get_contents($dataFile);
$dataList = json_decode($dataTxt,true);
$arrImg = array();
$stack = array();

$j = 0;
foreach($dataList['data'] as $indexItems){
	array_push($stack, $indexItems['index']);
	array_push($arrImg, $indexItems['img']);
	$j++;
}

$k = 0;
foreach($dataList['data'] as $indexItems){
	if (isset($_POST['reload'.$k])) {

		$pos = $dataList['data'][$k]['index'];
		$newTxt = $_POST["text$k"];
		$newImg =  $dataList['data'][$k]['img'];
		
		$dataArr = array('index'=>$pos,'text'=>$newTxt,'img'=>$newImg); 
		
		//array_unshift($dataList['data'], $dataArr);// this works
		array_splice($dataList['data'], -$pos, 0, $dataArr);//<< error
		unset($dataList['data'][$k+1]);
		
		
		$dataTxt = json_encode($dataList);
	}
	$k++;
}

[ggalan]

fixed:

array_splice($dataList['data'], -$pos, 0, array($dataArr))