How to create a new attribute using items from a list and append it back to the same list of dictionaries?

I have this list:

{
  "data": [
    {
      "ClassType": "Part Time",
      "FirstName": "Monice",
      "LastName": "Lee"
    },
    {
      "ClassType": "Full Time",
      "FirstName": "Henry Daley",
      "LastName": "Brown"
    }
  ]
}

How do I create a new attribute FullName, which value would be FirstName + ' ' + LastName and append this to all the dictionaries of the list?

Expected output:

{
 "data": [
    {
        "ClassType": "Part Time",
        "FirstName": "Monice",
        "LastName": "Lee",
        "FullName": "Monice Lee"
    },
    {
        "ClassType": "Full Time",
        "FirstName": "Henry Daley",
        "LastName": "Brown",
        "FullName": "Henry Daley Brown"
    }
 ]
}

I tried this approach:

- set_fact:
    FullName: "{{ item.FirstName + ' ' + item.LastName }}"
  loop: "{{ data }}"

However, the new variable ended up appearing under ansible_facts.FullName and not item.FullName.

Output

ok: [localhost] => (item={'FirstName': 'Henry Daley', 'LastName': 'Brown', 'ClassType': 'Full Time'}) => {
    "ansible_facts": {
        "FullName": "Henry Daley Brown"
    },
    "ansible_loop_var": "item",
    "changed": false,
    "item": {
        "ClassType": "Full Time",
        "FirstName": "Henry Daley",
        "LastName": "Brown"
    }
}
ok: [localhost] => (item={'FirstName': 'Monice', 'LastName': 'Lee', 'ClassType': 'Part Time'}) => {
    "ansible_facts": {
        "FullName": "Monice Lee"
    },
    "ansible_loop_var": "item",
    "changed": false,
    "item": {
        "ClassType": "Part Time",
        "FirstName": "Monice",
        "LastName": "Lee"
    }
}

How can I create/append this FullName attribute each dictionary of the list?

You could use the join function of JMESPath to update your dictionary.

Given the task:

- set_fact:
    data: >-
      {{
        data | json_query("
        [].{
          ClassType: ClassType,
          FirstName: FirstName,
          LastName: LastName,
          FullName: join(' ', [FirstName, LastName])}
        ")
      }}
  vars:
    data:
      - ClassType: Full Time
        FirstName: Henry Daley
        LastName: Brown
      - ClassType: Part Time
        FirstName: Monice
        LastName: Lee

Your data variable would be updated according to your need:

ok: [localhost] => changed=false 
  ansible_facts:
    data:
    - ClassType: Full Time
      FirstName: Henry Daley
      FullName: Henry Daley Brown
      LastName: Brown
    - ClassType: Part Time
      FirstName: Monice
      FullName: Monice Lee
      LastName: Lee

^{Note: the above output have been generated running the playbook with the option -v, which, amongst other useful information, shows the result of a set_fact task.}

Create list update

  update: "{{ data|json_query('[].[FirstName, LastName]')|
                   map('join', ' ')|
                   map('community.general.dict_kv','FullName') }}"

<hr>

<sup>

Optionally, the query below gives the same result

  fn_query: "[].{FullName: join(' ', [FirstName, LastName])}"
  update: "{{ data|json_query(fn_query) }}"

</sup>

<hr>

gives

  update:
  - FullName: Monice Lee
  - FullName: Henry Daley Brown

Update data

    - set_fact:
        data: "{{ data|zip(update)|map('combine') }}"

gives

  data:
  - ClassType: Part Time
    FirstName: Monice
    FullName: Monice Lee
    LastName: Lee
  - ClassType: Full Time
    FirstName: Henry Daley
    FullName: Henry Daley Brown
    LastName: Brown

<hr>

<sup>

Example of a complete playbook for testing

- hosts: localhost

  vars:

    data:
    - ClassType: Part Time
      FirstName: Monice
      LastName: Lee
    - ClassType: Full Time
      FirstName: Henry Daley
      LastName: Brown

    update: "{{ data|json_query('[].[FirstName, LastName]')|
                     map('join', ' ')|
                     map('community.general.dict_kv','FullName') }}"

  tasks:

    - debug:
        var: update
    - set_fact:
        data: "{{ data|zip(update)|map('combine') }}"
    - debug:
        var: data

</sup>

According your initial post

> ... it ended up appearing under ansible_facts.FullName and not item.FullName ...

That's correct and the expected behavior.

> How can I create/append this FullName variable to the list of item variables

Short answer, you can't. At least not in that way and or without changing the Python code of loop. This is because the loop variables are not under the control of the task. One could think about of that that the loop code is surrounding the task code. The task code is not aware of that there is a loop outside.

If interested in more details or debugging you may have a look into Print item from interactive debugger in Ansible.

The solution for your problem will be a more complex data manipulation without a loop and is shown in the other answers here.