export function round(v: number): number {

  return Math.round(v * 10) / 10;

}

export function avg(arr: any[], fn: (d: any) => number): string {

  if (arr.length === 0) return '\u2014';

  return (arr.reduce((s, d) => s + fn(d), 0) / arr.length).toFixed(1);

}

export function std(values: number[]): number {

  if (values.length < 2) return 0;

  const m = values.reduce((s, v) => s + v, 0) / values.length;

  const variance = values.reduce((s, v) => s + (v - m) ** 2, 0) / (values.length - 1);

  return Math.sqrt(variance);

}

/** Remove outliers using the IQR method, returns filtered array */

export function filterOutliers(values: number[], k = 1.5): number[] {

  if (values.length < 4) return values;

  const sorted = [...values].sort((a, b) => a - b);

  const q1 = sorted[Math.floor(sorted.length * 0.25)];

  const q3 = sorted[Math.floor(sorted.length * 0.75)];

  const iqr = q3 - q1;

  const lower = q1 - k * iqr;

  const upper = q3 + k * iqr;

  return values.filter((v) => v >= lower && v <= upper);

}