Find the name of a key whose attribute matches some string

filter.pp

$service_accounts = {
  'larry' => {
    gid   => '1111',
    tag   => 'group_a',
  },
  'moe' => {
    gid   => '2222',
    tag   => 'group_b',
  },
  'curly' => {
    gid   => '3333',
    tag   => 'group_c',
  },
}

$group_b_svc_account = $service_accounts.filter |$name, $attr| {
  $attr['tag'] == 'group_b'
}.keys[0]

notice($group_b_svc_account)

This also works, but is arguably harder to read...

$group_b_svc_account = $service_accounts.reduce |$memo, $user_array| {
  ($user_array[1]['tag'] == 'group_b') ? {
    true  => $user_array[0],
    false => $memo
  }
}

notice($group_b_svc_account)