ansible - example of pulling out all az:subnets pairs from facts

foo.json

[{
    "subnets": [
        {
            "availability_zone": "eu-west-1c",
            "available_ip_address_count": 29,
            "cidr_block": "<REDACTED>",
            "default_for_az": "false",
            "id": "subnet-<id>",
            "map_public_ip_on_launch": "false",
            "state": "available",
            "tags": {
                "Description": "subnet in AZc",
                "Name": "<subname>",
                "aws:cloudformation:logical-id": "subnetAZc",
                "aws:cloudformation:stack-id": "<verylongcfnid>",
                "aws:cloudformation:stack-name": "<weirdcfnstackname>"
            },
            "vpc_id": "vpc-<id>"
        }
    ]
},
{
    "subnets": [
        {
            "availability_zone": "eu-west-1d",
            "available_ip_address_count": 29,
            "cidr_block": "<REDACTED>",
            "default_for_az": "false",
            "id": "subnet-<id>",
            "map_public_ip_on_launch": "false",
            "state": "available",
            "tags": {
                "Description": "subnet in AZc",
                "Name": "<subname>",
                "aws:cloudformation:logical-id": "subnetAZc",
                "aws:cloudformation:stack-id": "<verylongcfnid>",
                "aws:cloudformation:stack-name": "<weirdcfnstackname>"
            },
            "vpc_id": "vpc-<id>"
        }
    ]
}]

output

PLAY [localhost] ***************************************************************************************************************************************************************************************************************************************************************

TASK [set_fact] ****************************************************************************************************************************************************************************************************************************************************************
ok: [localhost]

TASK [set_fact] ****************************************************************************************************************************************************************************************************************************************************************
ok: [localhost]

TASK [set_fact] ****************************************************************************************************************************************************************************************************************************************************************
ok: [localhost] => (item=[u'eu-west-1c', u'subnet-<id>'])
ok: [localhost] => (item=[u'eu-west-1d', u'subnet-<id>'])

TASK [debug] *******************************************************************************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "mydict": {
        "eu-west-1c": "subnet-<id>",
        "eu-west-1d": "subnet-<id>"
    }
}

PLAY RECAP *********************************************************************************************************************************************************************************************************************************************************************
localhost                  : ok=4    changed=0    unreachable=0    failed=0

play.yml

---
- hosts: localhost
  gather_facts: False
  tasks:
    - set_fact:
        myitems: "{{ lookup('file', 'foo.json')|from_json }}"

    - set_fact:
        myfilter: "{{ myitems|json_query('[].subnets[].[availability_zone, id]') }}"

    - set_fact:
        mydict: "{{ mydict|default({})|combine({item[0]: item[1]}) }}"
      with_items: 
        # myfilter is a nested list structure, so we pass it as an item, instead of doing
        # with_items: "{{ myfilter }}"
        - "{{ myfilter }}"        

    - debug: var=mydict