Ability to show gaps in data? about fl_chart

[Vingtoft]

How can I use null values?
If null is parsed as Y value, the following exception is thrown:

Unhandled Exception: type 'Null' is not a subtype of type 'double'

My use case requires valid X values with null Y values

[shamilovtim]

Definitely but I think it conveys the proper feeling from the business logic side. The users didn't chart something that they were supposed to do, which caused the problem.

We could offer settings to interpolate with a dashed line and/or a pure null option:

Pure null

Interpolated with a dashed line:

I would be happy to help with this feature if we go with flutter for our project

[shamilovtim]

@yongjhih nulls should be in the next release

[shamilovtim]

Hello @imaNNeoFighT,

Thanks for the library! It's great so far. Is it possible to get real nullable coordinates added without having to create multiple instances of lines? This is a standard feature of a lot of different charting libraries.

In almost all of them the best practice is:

{ x: 5, y: null },
{ x: 6, y: null }

See:

1. https://google.github.io/charts/flutter/example/line_charts/simple_nulls
2. https://formidable.com/open-source/victory/gallery/victory-line-with-null-data/

[yongjhih]

That's what I did for null spots:

Skip null spots:

() {
    return LineChart(LineChartData(
        lineBarsData: LineChartBarData(/* ... */).listWith(spots.splitByNull()),
        minX: spots.map((it) => it.x).min(), // optional: Avoid trimming to keep the original range of x-axis
        maxX: spots.map((it) => it.x).max(), // optional: Avoid trimming to keep the original range of x-axis
        // ...
    ));
}

extension LineChartBarDataX<T extends LineChartBarData> on T {
  /// Skip spots while [spots] contain null y
  List<T> listWith(Iterable<List<FlSpot>> lists) {
    final data = this;
    return lists.map((spots) => data.copyWith(spots: spots)).toList();
  }
}

extension IterableFlSpotX<T extends FlSpot> on Iterable<T> {
  Iterable<List<T>> splitByNull() => splitBy((it) => it.y == null);
}

/// ref. https://github.com/yongjhih/dartx/blob/77ef87a/lib/src/iterable.dart#L1012
extension IterableX<T> on Iterable<T> {
  Iterable<List<E>> splitBy(bool test(E it)) {
    final lists = fold<List<List<E>>>([[]], (that, it) {
      if (!test(it)) {
        that.last.add(it);
      } else {
        if (that.last.isNotEmpty) {
          that.add([]);
        }
      }
      return that;
    });

    return lists.where((it) => it.isNotEmpty);
  }
}

Interpolate with the dashes for null spots:

() {
    return LineChart(LineChartData(
        lineBarsData: LineChartBarData(/* ... */).listDashableWith(spots),
        minX: spots.map((it) => it.x).min(), // optional: Avoid trimming to keep the original range of x-axis
        maxX: spots.map((it) => it.x).max(), // optional: Avoid trimming to keep the original range of x-axis
        // ...
    ));
}

extension LineChartBarDataX<T extends LineChartBarData> on T {
  /// Skip spots while [spots] contain null y
  List<T> listWith(Iterable<List<FlSpot>> lists) {
    final data = this;
    return lists.map((spots) => data.copyWith(spots: spots)).toList();
  }

  /// Return simple dashed [T]
  T dashed({
    List<int> dashArray = const [1, 2],
    double opacity = 0.5,
  }) {
    return copyWith(
        dashArray: dashArray,
        belowBarData: belowBarData?.copyWith(
          colors: belowBarData?.colors?.map((it) => it. opacityFactor(opacity))?.toList(),
        ));
  }

  /// Dashed [spots] while which contain null y
  List<T> listDashableWith(Iterable<FlSpot> spots, {
    List<int> dashArray = const [1, 2],
    double opacity = 0.5,
  }) {
    final repeatedSpots = spots.repeatByNull();
    final _dashed = dashed(dashArray: dashArray, opacity: opacity);
    if (repeatedSpots.isNotEmpty) {
      return repeatedSpots.map((it) => it.first.dashed ? _dashed.copyWith(spots: it) : copyWith(spots: it)).toList();
    } else {
      final values = spots.map((it) => it.x);
      return <T>[
        _dashed.copyWith(spots: <FlSpot>[
          FlSpot(values.min() ?? 0, 0),
          FlSpot(values.max() ?? 0, 0),
        ])
      ];
    }
  }
}

extension IterableFlSpotX<T extends FlSpot> on Iterable<T> {
  Iterable<List<T>> splitByNull() => splitBy((it) => it.y == null);
}

extension IterableFlSpotsX on Iterable<FlSpot> {
  Iterable<List<FlSpotDashable>> repeatByNull() =>
      map((it) => FlSpotDashable(it.x, it.y))
          .repeatBy((it) => it.y == null, (that, it) => FlSpotDashable(that.x, that.y, dashed: true))
          .where((it) => it.isNotEmpty);
}

class FlSpotDashable extends FlSpot {
  const FlSpotDashable(double x, double y, {this.dashed = false}) : super(x, y);

  final bool dashed;

  @override
  FlSpotDashable copyWith({
    double x,
    double y,
    bool dashed = false
  }) {
    return FlSpotDashable(
      x ?? this.x,
      y ?? this.y,
      dashed: dashed ?? this.dashed,
    );
  }

  @override
  String toString() {
    return "{x: ${x}, y: ${y}, dashed: $dashed}";
  }
}

extension BarAreaDataX<T extends BarAreaData> on T {
  BarAreaData copyWith({
    bool show,
    List<Color> colors,
    Offset gradientFrom,
    Offset gradientTo,
    List<double> gradientColorStops,
    BarAreaSpotsLine spotsLine,
    double cutOffY,
    bool applyCutOffY,
  }) => BarAreaData(
      show: show ?? this.show ?? false,
      colors: colors ?? this.colors ?? const [Colors.blueGrey],
      gradientFrom: gradientFrom ?? this.gradientFrom ?? const Offset(0, 0),
      gradientTo: gradientTo ?? this.gradientTo ?? const Offset(1, 0),
      gradientColorStops: gradientColorStops ?? this.gradientColorStops,
      spotsLine: spotsLine ?? this.spotsLine ?? const BarAreaSpotsLine(),
      cutOffY: cutOffY ?? this.cutOffY,
      applyCutOffY: applyCutOffY ?? this.applyCutOffY ?? false,
    );
}

/// ref. https://github.com/yongjhih/dartx/blob/77ef87a/lib/src/iterable.dart#L1012
extension IterableX<T> on Iterable<T> {
  Iterable<List<E>> splitBy(bool test(E it)) {
    final lists = fold<List<List<E>>>([[]], (that, it) {
      if (!test(it)) {
        that.last.add(it);
      } else {
        if (that.last.isNotEmpty) {
          that.add([]);
        }
      }
      return that;
    });

    return lists.where((it) => it.isNotEmpty);
  }

  Iterable<List<T>> repeatBy(bool test(T it), T repeat(T repeater, T element)) {
    if (isEmpty) {
      return [[]];
    }

    final lists = skip(1).fold<List<List<T>>>([[first]], (that, it) {
      if (test(it)) { // it == null
        // repeating for current
        if (test(that.last.last)) { // it == null && last == null
          // skip
        } else { // it == null && last != null
          // repeat by repeater
          that.add([repeat(that.last.last, it), it]);
        }
      } else { // it != null
        if (test(that.last.last)) { // it != null && last == null
          that.last.last = repeat(it, that.last.last);
          that.add([it]);
        } else { // it != null && last != null
          that.last.add(it);
        }
      }

      return that;
    });

    if (test(lists.last.last)) { // it != null && last == null
      final repeater = lists.last.lastOrNullWhere((it) => !test(it));
      if (repeater != null) {
        lists.last.last = repeat(repeater, lists.last.last);
      }
    }

    return lists.where((it) => it.every((that) => !test(that)));
  }
}

extension ColorX<T extends Color> on T {
  Color opacityFactor(double factor) =>
      withOpacity(opacity * factor);
}

I'm still looking for this project will support the nullable spots by itself.

[imaNNeo]

You can have multiple bars on the LineChart, then make two separted and combine them in your chart,

[imaNNeo]

check LineBarsData , you can have multiple LineChartBarData

[stx]

Got it! Thank you!

[imaNNeo]

Okay fine, we need this in the line chart, but It is weird when we have rounded line chart

[imaNNeo]

Nice, we will consider it.
Thanks for reporting!

[imaNNeo]

Implemented in 0.8.6, check it out!

[cryosx]

How can I use null values? If null is parsed as Y value, the following exception is thrown:

Unhandled Exception: type 'Null' is not a subtype of type 'double'

My use case requires valid X values with null Y values

FlSpot.nullSpot