Question 109536 in Json Question posted in
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Json – How to join or unionize a list of list elements (unknown length)

I’m parsing some values using json_query. After extracting the values I’m left with a list of elements which contain the list of values. My goal is to have a single list of un-nested values.
How can I achieve this?

E.g.:

my_list: [ [1,2],[3,4],[5,6] ]

Should become

my_list: [1,2,3,4,5,6]

I can’t use my_list[0] | union([my_list[1]) | union(my_list[2]) because the my_list is dynamic.

Tags:

2

Answers


  1. 0

    You can use a custom plugin to handle Python-like jobs easily. To do this, create a folder named filter_plugins (make sure to use this reserved name) in the same folder as your playbook, and add your Python filter there.

    $ tree
├── nested_list.yml
├── filter_plugins
│   └── nested_union.py
└── inventory

    Make sure the filter contains the FilterModule class and filters method:

    $ cat nested_union.py
class FilterModule(object):
    def filters(self):
        return {
            'nested_union': self.nested_union,
        }

    def nested_union(self, nested_list):
        return [x for inner_list in nested_list for x in inner_list]

    Call the new filter from your Ansible playbook:

    ---
- name: 
  hosts: local
  tasks:
    - name: Union merged lists
      vars: 
        my_list: [ [1,2],[3,4],[5,6] ]
      set_fact:
        new_list: "{{ my_list | nested_union }}"
...

    Here is the inventory file, just for reference and to complete the example:

    [local]
127.0.0.1 ansible_connection=local

    And here is the result of the execution:

    $ ansible-playbook -i inventory nested_list.yml -v

-- snip --

TASK [Union merged lists]
ok: [127.0.0.1] => {"ansible_facts": {"new_list": [1, 2, 3, 4, 5, 6]}, "changed": false}
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  2. 0

    Use the flatten filter.

    Given:

    - debug:
    msg: "{{ [ [1,2],[3,4],[5,6] ] | flatten(1) }}"

    This yields the expected list:

    ok: [localhost] => 
  msg:
  - 1
  - 2
  - 3
  - 4
  - 5
  - 6

    And since you state that you are using json_query, note that there is also a way to flatten in JMESPath, called flatten projection, so you might bake this is your existing query.

    As an example:

    - debug:
    msg: "{{ [ [1,2],[3,4],[5,6] ] | json_query('[]') }}"

    Will also yield the expected result.

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