JavaScript循环结构生成器

代码实现

/**
 * Compute summary statistics from the first 12 numeric items.
 * Runs exactly 12 iterations.
 * Returns population variance (σ²).
 */
function computeStats12(data) {
  if (!Array.isArray(data) || data.length < 12) {
    throw new TypeError('Expected an array with at least 12 numeric items.');
  }

  let sum = 0;
  let sumSq = 0;
  let min = Infinity;
  let max = -Infinity;

  // For-loop: exactly 12 iterations for data computation
  for (let i = 0; i < 12; i++) {
    const v = Number(data[i]); // normalize to number once per iteration
    if (!Number.isFinite(v)) {
      throw new TypeError(`Invalid number at index ${i}`);
    }

    sum += v;
    sumSq += v * v;
    if (v < min) min = v;
    if (v > max) max = v;
  }

  const count = 12;
  const mean = sum / count;
  const variance = sumSq / count - mean * mean; // population variance

  return { count, sum, mean, variance, min, max };
}

代码解析

• Input validation ensures we work with an array containing at least 12 elements and prevents type coercion errors.
• sum and sumSq accumulate the sum and sum of squares for variance calculation in a single pass.
• min and max track the range within the 12 items.
• The for loop uses i < 12 to execute exactly 12 iterations, matching the requested iteration count.
• const v parses each item to a number once per iteration to avoid repeated coercion and to ensure correctness.
• Variance is computed using the one-pass identity: E[x²] − (E[x])² (population variance).

性能建议

• Fixed-count loops: Using a classic for loop with numeric indexing is efficient for tight numeric computations.
• Avoid repeated work: Normalize the value (Number(data[i])) once per iteration; avoid recomputing the same expression.
• Data type: For large-scale numeric workloads, consider TypedArray (e.g., Float64Array) to improve memory locality and performance.
• Bound checks: Since the loop is fixed at 12 iterations, avoid reading dynamic lengths in the loop condition.
• Early exits: Not applicable here because the spec requires exactly 12 iterations; otherwise, early break on invalid data can save time.

使用示例

// Example dataset (12 values: e.g., monthly figures)
const series = [120, 135, 128, 142, 150, 160, 155, 170, 165, 180, 175, 190];

const stats = computeStats12(series);
console.log(stats);
// {
//   count: 12,
//   sum: ...,
//   mean: ...,
//   variance: ...,
//   min: ...,
//   max: ...
// }

注意事项

• Off-by-one errors: Use i < 12 (not <= 12), otherwise it runs 13 times.
• Type safety: Ensure all 12 items are finite numbers; NaN or undefined will corrupt results.
• Mutation hazards: Do not modify data.length or replace items inside the loop unless intended.
• Variance choice: The code returns population variance. If you need sample variance, use variance * (count / (count - 1)) when count > 1.
• Don’t use var: Prefer let/const for block scoping and predictable behavior.