Replace array keys - php

Question

i have an array like this JSON Example .I'm trying to replace the numeric key ..."conn":{"1":{"... with string key such as "node".
FOR EXAMPLE i want to create this:
{
"Level": [
{
"main": "472321514",
"main_lat": "39.1057579",
"main_lon": "26.5451331",
"conn": {
"node": {
"id": "599416249",
"coords": {
"lat": "39.1055889",
"lon": "26.5452403"
},
"distance": 0.0209442235276
},...
Before json encoding my script is:
foreach ($ways as $w){
$nd=$w->nd;
foreach ($nd as $w2){
$nodes_Array[]=(string)$w2->attributes()->ref;
}
for($ww=0;$ww<count($nodes_Array);$ww++){
$nodes_Array2[$bb]['main'] = $nodes_Array[$ww];
for($gg=0;$gg<count($node_content);$gg++){
if($node_content[$gg]['id']==$nodes_Array2[$bb]['main']){
$nodes_Array2[$bb]['main_lat']= $node_content[$gg]['lat'];
$nodes_Array2[$bb]['main_lon']= $node_content[$gg]['lon'];
}
}
$nodes_Array2[$bb]['conn'] = array_diff($nodes_Array, array($nodes_Array[$ww]));
for($cc=0;$cc<count($nodes_Array2[$bb]['conn']);$cc++){
for($gg=0;$gg<count($node_content);$gg++){
if($node_content[$gg]['id']==$nodes_Array2[$bb]['conn'][$cc]){
$nodes_Array2[$bb]['conn'][$cc]=Array(
'id'=>$node_content[$gg]['id'],
'coords'=>Array(
'lat'=>$node_content[$gg]['lat'],
'lon'=>$node_content[$gg]['lon'],
),
'distance'=>distance($nodes_Array2[$bb]['main_lat'],$nodes_Array2[$bb]['main_lon'],$node_content[$gg]['lat'],$node_content[$gg]['lon'],"K"),
);
}
}
}
$bb++;
}
unset($nodes_Array);
}