Transforming an ansible list of lists to a list of dicts

I finally learned how to do nested lists with product, but I don't like that I have to access the results by indices. product produces a list of lists, and I want a list of dicts.

For example, the following code....

- name: experimenting
  hosts: localhost
  tasks:
  - name: Define some facts
    set_fact:
      people:
      - name: "Fred"
      - name: "John"
      animals:
      - name: "cat"

  - debug:
      msg: "{{ animals | product(people)  }}"  

...produces the following output:

ok: [localhost] => {
    "msg": [
        [
            {
                "name": "cat"
            },
            {
                "name": "Fred"
            }
        ],
        [
            {
                "name": "cat"
            },
            {
                "name": "John"
            }
        ]
    ]
}

How can I transform that so it looks like:

ok: [localhost] => {
    "msg": [
        {
            animal: {
                name: "cat"
            },
            person: {
                name: "Fred"
            }
        },
        {
            animal: {
                name: "cat"
            },
            person: {
                name: "John"
            }
        }
    ]
}

In C#, I would use the LINQ Select statement, but I can't find the equivalent of that in ansible world.

That one is not written using chatGPT as it is (at least temporarily) forbidden by site rules. Moreover, it includes some fixes on your initial question to respect best practice like using set_facts only when it is needed and looping in a task only when necessary.

This self explanatory playbook with intermediate debug should be quite easy to get and gives what you expect:

---
- name: experiment
  hosts: localhost
  gather_facts: false

  vars:
    
    people:
      - name: "Fred"
      - name: "John"
    
    animals:
      - name: "cat"

    people_as_dict: "{{ ['people: '] | product(people) | map('join') | map('from_yaml') }}"

    animals_as_dict: "{{ ['animal: '] | product(animals) | map('join') | map('from_yaml') }}"

    people_animals: "{{ people_as_dict | product(animals_as_dict) | map('combine') }}"

  tasks:
    - name: Tranform people list so that each element is a dict
      ansible.builtin.debug:
        var: people_as_dict

    - name: Do the same thing as above with animals
      ansible.builtin.debug:
        var: animals_as_dict

    - name: combine every element to get expected resutl
      ansible.builtin.debug:
        var: people_animals

Demo run:

PLAY [experiment] ******************************************************************************************************************************************************************************************

TASK [Tranform people list so that each element is a dict] *************************************************************************************************************************************************
ok: [localhost] => {
    "people_as_dict": [
        {
            "people": {
                "name": "Fred"
            }
        },
        {
            "people": {
                "name": "John"
            }
        }
    ]
}

TASK [Do the same thing as above with animals] *************************************************************************************************************************************************************
ok: [localhost] => {
    "animals_as_dict": [
        {
            "animal": {
                "name": "cat"
            }
        }
    ]
}

TASK [combine every element to get expected resutl] ********************************************************************************************************************************************************
ok: [localhost] => {
    "people_animals": [
        {
            "animal": {
                "name": "cat"
            },
            "people": {
                "name": "Fred"
            }
        },
        {
            "animal": {
                "name": "cat"
            },
            "people": {
                "name": "John"
            }
        }
    ]
}

PLAY RECAP *************************************************************************************************************************************************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

I figured it out.

- name: experimenting
  hosts: localhost
  tasks:
  - name: Define some facts
    set_fact:
      people:
      - name: "Fred"
      - name: "John"
      animals:
      - name: "cat"

  - name: Transform the data
    set_fact:
      transformed: "{{ transformed | default([]) + [{'animal': item[0], 'person': item[1] }] }}"
    loop: "{{ animals | product(people) }}"

  - debug:
      msg: "{{ transformed }}"

...produces:

ok: [localhost] => {
    "msg": [
        {
            "animal": {
                "name": "cat"
            },
            "person": {
                "name": "Fred"
            }
        },
        {
            "animal": {
                "name": "cat"
            },
            "person": {
                "name": "John"
            }
        }
    ]
}