Get values of dynamically add select dropdown multiple values in Laravel 9 - php

Question

I have 2 Select options which are as follow:
<select name="attribute[]" id="attribute" data-id="1" >
<option value="1">Size</option>
<option value="2">Color</option>
</select>
<select name="attribute_value[]" id="attribute_value1" multiple>
<option value="0">Please Select</option>
<select>
and attribute value popup with ajax when change option on attribute
$(document).on('change','.attribute', function() {
let attr_id = $(this).val();
let rowId = $(this).data('id');
$.ajax({
url:"{{ route('admin.getAttributeValue')}}",
type:"post",
data:{
_token:'{{ csrf_token() }}',
id:attr_id,
},
success:function(response){
if(response)
{
var data = JSON.parse(response);
$('#attribute_value'+rowId).empty().append('<option value="0">Please Select value</option>');
for (var key in data) {
$('#attribute_value'+rowId).append('<option value="'+key+'" >'+data[key]+'</option>');
}
}else{
$('#attribute_value'+rowId).empty().append('<option value="0">Please Select value</option>');
}
}
});
});
and in controller
public function getAttributeValue(Request $request)
{
$values = AttributeValue::where('attribute_id',$request->id)->get();
if(count($values))
{
$v=[];
foreach($values as $val)
{
$v[$val->id]=$val->value;
}
return json_encode($v);
}
}
and on button click its add Row
<a href='#' onclick="add_more()">Add Row<a/>
x=1;
function add_more()
{
var wrapper = $('#product_attribute');
var html = '<div class="card " id="c'+x+'"><div class="card-body"><div class="row">';
var attribute = $('#attribute').html();
attribute = attribute.replace("selected","");
var attr = '<div class="col-2"><select name="attribute[]" id="attribute" data-id="'+x+'" class="attribute form-control">'+attribute+'</select></div>';
html += attr;
var val = '<div class="col-3"><select multiple name="attribute_value[]" id="attribute_value'+x+'" class="form-control"><option value="0">Please Select</option></select></div>';
html += val;
html += '</div></div></div>';
wrapper.append(html);
x++;
}
My problem is that
when the form submit the data shows me in this format
Attribute Array
$request->attribute = Array
(
[0] => 1
[1] => 2
)
Attribute value Array
$request->attribute_value = Array
(
[0] => 1
[1] => 2
[2] => 4
[3] => 5
[4] => 6
)
In above example I select 2 Values for Size and 3 values for Color
I want to data like in this format
like for each attribute has a array of attribute values
$arr = [];
arr[1] = [1,2],
arr[2] = [4,5,6]
Can any body help me in this matter. Thanx