Extract a whole dictionary from a list of dictionaries by value

Question

I need to extract a whole dictionary from a list of dictionaries based on a value.

"msg": [
    {
        "duplicate_key": "in dict_name_one",
        "KEY_1_dict_name_one": "VALUE_1_dict_name_one",
        "KEY_2_could_be anything": "VALUE_2_dict_name_one",
        "dict_name": "dict_name_one"
    },
    {
        "duplicate_key": "in dict_name_two",
        "KEY_1_second_dict": "VALUE_1_second_dict",
        "KEY_2_d_two": "VALUE_2_could_be anything",
        "dict_name": "dict_name_two"
    }
]

I would like to match on the Value of "dict_name" (when dict_name == dict_name_two)and get only dictionary containing that match back.

{
    "duplicate_key": "in dict_name_two",
    "KEY_1_second_dict": "VALUE_1_second_dict",
    "KEY_2_d_two": "VALUE_2_could_be anything",
    "dict_name": "dict_name_two"
}

The only constant is here is the Key "dict_name".

I already have a loop and a rejectattr on dict_name to set a bunch of facts off the remaining key/values pairs.

Vladimir Botka · Answer 1 · 2023-04-30T07:48:34.737

^{Given the list
l0:
- KEY_1_dict_name_one: VALUE_1_dict_name_one
KEY_2_could_be anything: VALUE_2_dict_name_one
dict_name: dict_name_one
duplicate_key: in dict_name_one
- KEY_1_second_dict: VALUE_1_second_dict
KEY_2_d_two: VALUE_2_could_be anything
dict_name: dict_name_two
duplicate_key: in dict_name_two
- KEY_1_second_dict: VALUE_1_second_dict
KEY_2_d_two: VALUE_2_could_be anything
duplicate_key: in dict_name_two

remove the items where the attribute dict_name is missing
l1: "{{ l0|rejectattr('dict_name', 'undefined') }}"

gives
l1:
- KEY_1_dict_name_one: VALUE_1_dict_name_one
KEY_2_could_be anything: VALUE_2_dict_name_one
dict_name: dict_name_one
duplicate_key: in dict_name_one
- KEY_1_second_dict: VALUE_1_second_dict
KEY_2_d_two: VALUE_2_could_be anything
dict_name: dict_name_two
duplicate_key: in dict_name_two}

There are more options. If the values of the attribute dict_name are unique create the dictionary

  d1: "{{ dict(l1|map(attribute='dict_name')|zip(l1)) }}"

gives

  d1:
    dict_name_one:
      KEY_1_dict_name_one: VALUE_1_dict_name_one
      KEY_2_could_be anything: VALUE_2_dict_name_one
      dict_name: dict_name_one
      duplicate_key: in dict_name_one
    dict_name_two:
      KEY_1_second_dict: VALUE_1_second_dict
      KEY_2_d_two: VALUE_2_could_be anything
      dict_name: dict_name_two
      duplicate_key: in dict_name_two

The search is trivial now.

^{Example of a complete playbook for testing
- hosts: localhost

vars:

l1:
- KEY_1_dict_name_one: VALUE_1_dict_name_one
KEY_2_could_be anything: VALUE_2_dict_name_one
dict_name: dict_name_one
duplicate_key: in dict_name_one
- KEY_1_second_dict: VALUE_1_second_dict
KEY_2_d_two: VALUE_2_could_be anything
dict_name: dict_name_two
duplicate_key: in dict_name_two

d1: "{{ dict(l1|map(attribute='dict_name')|zip(l1)) }}"

tasks:

- debug:
var: l1
- debug:
var: d1}

The next option is either the filter selectattr or json_query

    - debug:
        msg: "{{ l1|selectattr('dict_name', 'eq', 'dict_name_two') }}"

    - debug:
        msg: "{{ l1|json_query('[?dict_name == `dict_name_two`]') }}"

Both options provide a list of the selected dictionaries because there might more items with the same value of the attribute dict_name

  msg:
  - KEY_1_second_dict: VALUE_1_second_dict
    KEY_2_d_two: VALUE_2_could_be anything
    dict_name: dict_name_two
    duplicate_key: in dict_name_two

If you want to substitute a variable the expressions below give the same results

    - debug:
        msg: "{{ l1|selectattr('dict_name', 'eq', dict_name) }}"
      vars:
        dict_name: dict_name_two

    - debug:
        msg: "{{ l1|json_query(_query) }}"
      vars:
        dict_name: dict_name_two
        _query: '[?dict_name == `{{ dict_name }}`]'

^{Example of a complete playbook for testing
hosts: localhost

vars:

l1:
- KEY_1_dict_name_one: VALUE_1_dict_name_one
KEY_2_could_be anything: VALUE_2_dict_name_one
dict_name: dict_name_one
duplicate_key: in dict_name_one
- KEY_1_second_dict: VALUE_1_second_dict
KEY_2_d_two: VALUE_2_could_be anything
dict_name: dict_name_two
duplicate_key: in dict_name_two

tasks:

- debug:
msg: "{{ l1|selectattr('dict_name', 'eq', 'dict_name_two') }}"
- debug:
msg: "{{ l1|json_query('[?dict_name == `dict_name_two`]') }}"

- debug:
msg: "{{ l1|selectattr('dict_name', 'eq', dict_name) }}"
vars:
dict_name: dict_name_two
- debug:
msg: "{{ l1|json_query(_query) }}"
vars:
dict_name: dict_name_two
_query: '[?dict_name == `{{ dict_name }}`]'}

That worked perfectly, of course! What failed was a rejectattr that I omitted in the original question, that wasn't removing a dict in the list that didn't have the "dict_name" key, — RearAdmiralLieutenantGeneralRi, Apr 30 '23 at 05:42

Extract a whole dictionary from a list of dictionaries by value

1 Answers1