3.1-math.js使用

优化数据的计算
https://mathjs.org/docs/reference/functions.html

1、均值，方差，标准差

      const x = item.data;
      x.sort((a, b) => a - b);
      const total = x.length;
      const sum = x.reduce((t, n) => t + n);
      const min = x[0];
      const max = x[total - 1];
      const mean = Math.round(sum / total);
      let median = 0;
      if (total % 2) {
        median = x[(total - 1) / 2];
      } else {
        median = (x[total / 2 - 1] + x[total / 2]) / 2;
      }
      const stdDevSum = x.map(a => (a - mean) * (a - mean)).reduce((t, n) => t + n);
      const stdDev = Math.sqrt(stdDevSum / (total - 1)).toFixed(6);
      stats.push([item.name, min, max, mean, median, stdDev]);

math的方法，可以接收arr也可以接收...arr

        math.min(x),
        math.max(x),
        Math.round(math.mean(x)),
        Math.round(math.median(x)),
        math.std(x).toFixed(6),

2、随机数

math.pickRandom([3, 6, 12, 2])   // returns one of the values in the array
random(100) //  有小数
randomInt(20,25) //  有20没有25