Returns a group with the top verbs.  activities - All activities count      - How many verbs to show  Returns a list of top verbs plus 'other'
function topVerbs(activities, count) {
    var counts = {},
        list = [],
        top;
    for (var i in activities) {
      var verb = activities[i].verb;
      counts[verb] = (counts[verb] || 0) + 1;
    }
    for (key in counts)
      list.push({ key: key, values: counts[key] });
    top = list.sort(function(a, b) { return b.values - a.values })
      .slice(0, count)
      .map(function(verb) { return verb.key })
      .concat("other");

    // Make sure all verbs are showing by default.
    verbsShowing = top.reduce(function(showing, verb) {
      showing[verb.key] = verbsShowing[verb];
      if (showing[verb] == undefined)
        showing[verb] = true;
      return showing;
    }, {});

    return top;
  }