Ansible - join / flatten a dict of lists

Question

I have a dict of lists such as here, though the inner data could be any level of complexity (perhaps strings, perhaps dicts, perhaps multi layer nested complex object).

my_dict:
  my_list_a:
    - a
    - b
    - c
  my_list_b:
    - a
    - d
    - e
  list_c:
    - f

1. How do I flatten this structure / join the inner items into a list in the following format through jinja2 (preserving order is not important to me in my current use case but it's always nice when possible).

my_combined_list:
  - a
  - b
  - c
  - a
  - d
  - e
  - f

Unfortunately as list comprehensions are out of the question due to lack of support in Jinja, I haven't been able to piece a solution together so far.

There are also some extra things I need to do, though most are easily doable on the final list (deduplicate, sort, etc). Something that needs to be done during the join is:

2. select or reject based on a test (e.g. only include lists that start with string: my_ meaning list_c is not added to the end result)

I've found many ways for list of dicts, or various more complex special cases, but I can't seem to find anything on making a list of all inner items of a dict of lists of items.

Answer 1

Q: Flatten the inner items into a list.

A: The simplest option is

my_combined_list: "{{ my_dict.values() | flatten }}"

gives

my_combined_list: [a, b, c, a, d, e, f]

Q: Select or reject based on a test (start string: my_ , e.g. list_c is omitted).

A: For example, use the test match

allow_match: [my_]
my_combined_list: "{{ my_dict | dict2items |
                      selectattr('key', 'match', allow_match|join('|')) |
                      map(attribute='value') | flatten }}"

gives

my_combined_list: [a, b, c, a, d, e]

---

Example of a complete playbook for testing

- hosts: localhost

  vars:

    my_dict:
      my_list_a: [a, b, c]
      my_list_b: [a, d, e]
      list_c: [f]

    my_combined_list: "{{ my_dict.values() | flatten }}"
    allow_match: [my_]
    my_combined_lis2: "{{ my_dict | dict2items |
                          selectattr('key', 'match', allow_match|join('|')) |
                          map(attribute='value') | flatten }}"

  tasks:

    - debug:
        var: my_combined_list | to_yaml
    - debug:
        var: my_combined_lis2 | to_yaml