c# 中的性能优化循环字符串连接

Question

我有一个处理一些历史数据的应用程序。我做了一些性能分析，并将以下功能确定为新的瓶颈：

public string GenerateSaveStringOptimized()
{
    StringBuilder saveString = new StringBuilder();
    saveString.Append( $"{this.TimeOfDay},{this.DayOfMonth},{this.DayOfYear},");
    foreach (float value in this.MovingAverage3h) saveString.Append($"{value},");
    foreach (float value in this.MovingAverage6h) saveString.Append($"{value},");
    foreach (float value in this.MovingAverage1d) saveString.Append($"{value},");
    foreach (float value in this.MovingAverage6d) saveString.Append($"{value},");
    foreach (float value in this.MovingAverage12d) saveString.Append($"{value},");
    foreach (float value in this.MovingAverage24d) saveString.Append($"{value},");
    foreach (float value in this.MovingAverage48d) saveString.Append($"{value},");
    foreach (float value in this.MovingAverage96d) saveString.Append($"{value},");
    foreach (float value in this.RSI3h) saveString.Append($"{value},");
    foreach (float value in this.RSI6h) saveString.Append($"{value},");
    foreach (float value in this.RSI1d) saveString.Append($"{value},");
    foreach (float value in this.RSI6d) saveString.Append($"{value},");
    foreach (float value in this.RSI12d) saveString.Append($"{value},");
    foreach (float value in this.Momentum1h) saveString.Append($"{value},");
    foreach (float value in this.SpotPrices1h) saveString.Append($"{value},");
    foreach (float value in this.BuyPrices1h) saveString.Append($"{value},");
    foreach (float value in this.SellPrices1h) saveString.Append($"{value},");
    saveString.Append($"{this.Label}");
    return saveString.ToString();
}

结果将是一个 csv 格式的字符串，例如：

0,1,1,0.4916667,0.4916667,0.4916667,0.4916667,0.4916667,0.49,0.49,0.49,0.49,0.4897351, [...]

每个数组都包含 25 个浮点值，因此代码类似于以下伪代码：

for (int i = 0; i < 17; i++)
{
    for (b = 0; b < 25 b++)
    {
        saveString.Append("Value,")
    }
}

每次调用该函数都会产生 17 * 25 = 425 个字符串连接！

有什么办法可以优化吗？

Top performance eater 似乎正在“等待 cpu”和“AppendformatHelper”，它是 StringBuilder 的内置方法。不幸的是，我不知道如何轻松处理

也许使用如下硬编码设置？

saveString.Append($"{MA3h[0]},{MA3h[1]},{MA3h[2]},...");
saveString.Append($"{MA6h[0]},{MA6h[1]},{MA6h[2]},...");
saveString.Append($"{MA1d[0]},{MA1d[1]},{MA1d[2]},...");

改用以下循环取得了巨大的成功：

foreach (float value in this.RSI1d)
{
    saveString.Append(value.ToString());
    saveString.Append(',');
}

非常感谢 user1672994、Guru Stron 和 Theodor Zoulias

评论中提到的其他内容也会尝试。

Answer 1

预分配足够的容量。

StringBuilder saveString = new StringBuilder(100000);

不要使用格式或插值。

saveString.Append(this.TimeOfDay).Append(',').Append(this.DayOfMonth).Append(',').Append(this.DayOfYear).Append(',');

在所有循环中执行类似的替换。

foreach (float value in this.MovingAverage3h) saveString.Append(value).Append(',');

不要使用格式或插值。

saveString.Append(this.Label);

Append方法有一个接受float的重载，所以不会有装箱。

c# 中的性能优化循环字符串连接

Performance optimizing looped string concatenations in c#

c#

string

performance

string-concatenation