  var evaluate = function ( truth, guess ) {
    // If prediction failed then return false!
    if ( guess === unknown || !labelsObj[ truth ] || !labelsObj[ guess ] ) return false;
    // Update confusion matrix.
    if ( guess === truth ) {
      cm[ truth ][ guess ] += 1;
    } else {
      cm[ guess ][ truth ] += 1;
    }
    evaluated = true;
    return true;
  }; // evaluate()