output

 /tmp/ansible_test  ansible-playbook-3 playbook.yml
 [WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'


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

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

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

TASK [debug] **************************************************************************************************************************************************
ok: [localhost] => {
    "openshift_node_group_labels": [
        [
            "node-role.kubernetes.io/master='true'",
            "node-role.kubernetes.io/infra='true'"
        ]
    ]
}

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

TASK [debug] **************************************************************************************************************************************************
ok: [localhost] => {
    "lbls": [
        "node-role.kubernetes.io/master='true'",
        "node-role.kubernetes.io/infra='true'"
    ]
}

PLAY RECAP ****************************************************************************************************************************************************
localhost                  : ok=5    changed=0    unreachable=0    failed=0   

playbook

---
- hosts: localhost
  gather_facts: false
  tasks:
  - set_fact:
      openshift_node_groups:
      - name: "node-config-master"
        labels:
        - node-role.kubernetes.io/master='true'
        - node-role.kubernetes.io/infra='true'
      - name: "node-config-node"
        labels:
        - node-role.kubernetes.io/compute='true'
  - set_fact:
      openshift_node_group_labels: "{{ openshift_node_groups | selectattr('name', 'match', 'node-config-master') | map(attribute='labels') | list }}"
  - debug: var=openshift_node_group_labels
  - set_fact:
      lbls: "{{ openshift_node_group_labels|join(',') }}"
  - debug: var=lbls