JQ Cannot iterate over null

I am trying to create a jq that is dynamic in returning data. User Story: I have data with many fields and not named like I want. I want to be able to based on the data and schema transform the data.

Example: JSON

  "inputArray": [
    {
      "objective_id": "ac-1_obj.a-1",
      "description": "an access control policy is developed and documented;",
      "framework_id": 1,
      "domain_id": "ac",
      "domaintitle": "Access Control",
      "id": 0,
      "control_id": "ac-1",
      "controltitle": "Policy and Procedures"
    },
    {
      "objective_id": "ac-1_obj.a-2",
      "description": "the access control policy is disseminated to {{ insert: param, ac-01_odp.01 }};",
      "framework_id": 1,
      "domain_id": "ac",
      "domaintitle": "Access Control",
      "id": 0,
      "control_id": "ac-1",
      "controltitle": "Policy and Procedures"
    },
    {
      "objective_id": "ac-1_obj.a-3",
      "description": "access control procedures to facilitate the implementation of the access control policy and associated controls are developed and documented;",
      "framework_id": 1,
      "domain_id": "ac",
      "domaintitle": "Access Control",
      "id": 0,
      "control_id": "ac-1",
      "controltitle": "Policy and Procedures"
    }
  ],
  "schema": [
    { "new": "objective", "input": "objective_id" },
    { "new": "framework", "input": "framework_id" },
    { "new": "control", "input": "control_id" },
    { "new": "title", "input": "controltitle" },
    { "new": "description", "input": "description" }
  ]
}

JQ

  inputArray: [
    .inputArray[] |
    reduce (.schema[] | {new: .new, input: .input}) as $map (
      {}; 
      .[$map.new] = .[$map.input]
    )
  ]
}

Error

jq: error (at /tmp/data.json:40): Cannot iterate over null (null) undefined

• schema is what it seems to be mad about.
• I have tested that .schema is available
• I have added ? to the end of .schema and values are empty

The error you are encountering is related to referencing the top level schema object while iterating through the contents of inputArray without having a proper reference back to it.

So, you need to be able to get the value of the current item with the key (item[ that maps to the key in the schema.

Try this:

{
  transformedArray: (
    [.inputArray[] as $item |
      reduce .schema[] as $s (
        {}; 
        . + { ($s.new): $item[$s.input] }
      )
    ]
  )
}

$item is the current item being iterated over in inputArray.
$s is the schema, then $s.new is the new key that replaces the old key $s.input.
The value is then obtained with $item[$s.input]