remove_duplicates.js

/*
 * Given array `records` and function `fn`
 * returns an array where 
 * any records with duplicate `fn(record)` values
 * are omitted.
 *
 * Runs in O(n) where n is records.length
 */
function remove_duplicates (records, fn) {
  var uniques = {},
      results = [];

  records.forEach(function (record) {
    var property = fn(record),
        has_property = uniques[property];

    if (!has_property) {
      // add to results
      results.push(record);
      // indicate that we've already seen this value
      uniques[property] = true;
    }
  });

  return results;
}

// for example
var records = [...]
records = remove_duplicates(records, function (record) {
  return record.rawDataChecksum;
});