View source for Run play only if host is reachable

Create a new group of the reachable hosts:    didnt work
<source lang="yaml">
- name: check reachable hosts
  hosts: all
  gather_facts: no
  tasks:
    - command: ping -c1 {{ inventory_hostname }}
      delegate_to: localhost
      register: ping_result
      ignore_errors: yes
    - group_by: key=reachable
      when: ping_result|success
</source>
The play that should be run only on reachable hosts:     ( didn't get this to work ) 
<source lang="yaml">
- name: your actual play
  hosts: reachable
  gather_facts: yes
  tasks:
    - debug: msg="this is {{ ansible_hostname }}"
</source>