quantileBoundaries function

List<num> quantileBoundaries(List<num> values, int bins)

The bins-1 internal cut points splitting sorted values into bins roughly equal-count groups (quantile boundaries).

Returns an empty list when bins < 2 or values is empty (no internal cut exists). Each boundary is the value at the corresponding quantile position in the ascending-sorted data. Audited: 2026-06-12 11:26 EDT

Implementation

List<num> quantileBoundaries(List<num> values, int bins) {
  assert(bins >= 1, 'quantileBoundaries requires bins >= 1');
  // One bin (or fewer) and empty input both have no internal cut points.
  if (bins < 2 || values.isEmpty) return <num>[];
  final List<double> sorted = values.map((num v) => v.toDouble()).toList()..sort();
  final List<num> cuts = <num>[];
  // The k-th cut sits at the k/bins fraction of the sorted data.
  for (int k = 1; k < bins; k++) {
    final int index = (sorted.length * k / bins).floor().clamp(0, sorted.length - 1);
    cuts.add(sorted[index]);
  }
  return cuts;
}