Column value as index to generate 2 level collection - laravel

Question

I am trying to get a collection which has index as column values.
First level will have product_id as index and second level will have stock_date.
$data = Model::select('column1', 'product_id', 'stock_date')
->where('some condition')
->get();
$data = collect($data)->groupBy('product_id');
With the code above, I get the collection with product_id as the indexes.
I need the data of each product indexed by stock_date
If, for example, for product_id - 1, I have multiple records, I tried
$product_details = collect($data[1])->groupBy('stock_date');
But it does not index the records with stock_date further.
Need help to index them with stock_date.

Answer 1

possible solution.
// first index grouped by product_id
$original = Model::select('column1', 'product_id', 'stock_date')
->where('some condition')
->get()
->groupBy->product_id;
$final = collect();
// iterate through each group and
// group inner collection with 'stock_date'
// and put them back in an collecion
foreach($original as $key => $value) {
$final->put($key, $value->groupBy->stock_date);
}

Answer 2

Do you means these records are nested by stock_date,
and then stock_dates are nested by product_id
If it is, please try this below, the collect() method make all nested records becomes collection, you don't need to use collect() again.
$data = Model::select('column1', 'product_id', 'stock_date')
->where('some condition')
->get();
$data = collect($data)->groupBy('product_id');
$nested_products = [];
foreach($data as $product_id => $items) {
$nested_products []= $items->groupBy('stock_date');
}
Or you can try this line, it's more elegant:
collect($data)->groupBy('product_id')->transform(function($item, $k) { return $item->groupBy('stock_date');})