dedupeTweets.js

var _ = require('underscore');

// getDupeList([Tweet]) -> { String : [Int] }
// runs in O(n+m) where n is # tweets, m is # dupes
function getDupeList(ts){
  var tts =_.chain(ts)
        .map(function(t,i){ return _.extend(t, { i: i });})
        .groupBy(function(tt){ return tt.id_str;})
        .value();
  return _.chain(tts)
    .keys()
    .filter(function(k){ return tts[k].length > 1; })
    .map(function(kk){
      return [kk, _.map(tts[kk], function(tt){
        return tt.i;})];})
    .object()
    .value();
}

//test getDupeList
(function(){
  var tweets = [
    { _id: 1, id_str: "123"},
    { _id: 2, id_str: "123"},
    { _id: 3, id_str: "456"},
    { _id: 4, id_str: "123"},
    { _id: 5, id_str: "456"},
    { _id: 6, id_str: "789"}
  ];
  var expected = {
    "123": [0,1,3],
    "456": [2,4]
  };
  var actual = getDupeList(tweets);
  if (_.isEqual(actual,expected)){ console.log("PASSING: getDupeList()"); }
  else {
    console.log("FAILED: getDupeList()");
    console.log("-- expected: ", expected);
    console.log("-- actual: ", actual);
  }
})();