Add user to a group after the user makes a comment in that group is this possible in Drupal Commons (Drupal 7) using Rules:

If a user makes a comment on a post in a certain group, have a rule which makes the user a member of the group automatically.

Why do I want to do this? Well, the contributors block in Drupal Commons is not showing all those who comment in a group. I found that the reason for this was that the particular user is not yet listed as an active member of the group.

Thank you!
The answer is ... yes, it is possible ... and easy to do ... with Rules.

If anyone coming across this is new to Rules or needs a refresher I highly recommend Johan Falk's free screencast series. It's excellent. http://nodeone.se/en/learn-the-rules-framework

See the screenshot for how I did it, and also the exported Rule below.

{ "rules_lambeth_comment_join_group" : {
"LABEL" : "lambeth comment join group",
"PLUGIN" : "reaction rule",
"REQUIRES" : [ "rules", "og", "comment" ],
"ON" : [ "comment_insert" ],
"IF" : [
  { "entity_has_field" : { "entity" : [ "comment:node" ], "field" : "og_group_ref" } }
],
"DO" : [
  { "og_subcribe_user" : {
      "user" : [ "comment:author" ],
      "group" : [ "comment:node:og-group-ref:0" ]
    }
  }
]
}
}