anchor.diff:    var first = xs.first;
     var high = xs.first;
     var low = xs.first;
  -  var close;
  -  xs.forEach((x) {
  +  late num close;
  +  for (var x in xs) {
       if (x > high) high = x;
       if (x < low) low = x;
       close = x;
  -  });
  +  }
     return <String, num>{'open': first, 'high': high, 'low': low, 'close': close};
   }
   
  
positive.code: Map<String, num> summary(Iterable<num> x, {bool Function(num)? isValid}) {
    isValid ??= (num x) => x.isNaN ? false : true;
    var q = Quantile(x.where(isValid).toList(growable: false));
    var probs = [0, 0.25, 0.5, 0.75, 1];
    var res = probs.map((p) => q.value(p)).toList();
    res.insert(3, mean(x));
    var names = ['Min.', '1st Qu.', 'Median', 'Mean', '3rd Qu.', 'Max.'];
  
negative.code:   var count = 0;
    var mean = 0.0;
    var sum = 0.0;
    num delta;
    for (var x in xs) {
      delta = x - mean;
      mean += delta / ++count;
  