code: function processDepKey(deps) {
    return Object.keys(deps)
      .reduce(reduceKeyToChanges, {});
  
    function reduceKeyToChanges(reduced, oldKey) {
  
      // replace in the row
      var value = deps[oldKey];   // value will be an index
      var newKey = String(value);   // use this index as the new key
      deps[newKey] = value;
      delete deps[oldKey];
  
      // record the replacement in the hash that is reduced
      reduced[oldKey] = newKey;
      return reduced;
    }
  }
docs: Replace each key in the <code>row.deps</code> with the value index and return a hash of replacements
  @param {object} deps A deps hash from a row
  @returns {object} A hash of replacements that were made