How to merge the contents of two collections?

Question

Laravel

There are two collections( $itemsByMart , $customProductsByMart ). Below is the screenshot of the code

return [
            '$itemsByMart' => $itemsByMart,
            '$customProductsByMart' => $customProductsByMart
        ];

I want to combine all the contents of two collections into one, but merge is not suitable, because I need the following output

{
  "1": [
     {...},
     {...},
     {...}
  ],
  "2": [
     {...}
  ],
  "3": [
     {...}
  ]
}

Please tell me how to get this result.

Answer 1

One new empty collection and two foreach - one for each existing one.