expandingMin method
Computes the expanding minimum for a column.
Implementation
List<double> expandingMin(int columnIndex) {
final data = filterNulls(columnIndex);
final n = data.length;
final result = List<double>.filled(n, double.nan);
if (n == 0) return result;
double m = data[0];
result[0] = m;
for (var i = 1; i < n; i++) {
if (data[i] < m) m = data[i];
result[i] = m;
}
return result;
}