我有一个这样的查找:
Lookup<String, pages> plsBase = (Lookup<String, pages>)(Query<pages>($@"Select ...").ToLookup(s => s.ip, o => o));
当我通过按键访问它时速度非常快,但问题是我需要使用 StartsWith() 来访问它。 当我像下面一样使用 StartsWith() 时,性能与常规列表相当
var pls = plsBase.Where(x => (x.Key.StartsWith(classBIp, StringComparison.Ordinal))).SelectMany(x => x).ToList();
问题是使用 StartsWith() 时可以采取什么措施来提高性能?
最佳答案
此答案假设 classBIp
具有固定长度。
选项 1:中间查找[已更新]
using System.Collections.Generic;
using System.Linq;
using NUnit.Framework;
namespace LookupTest
{
public class Tests
{
[Test]
public void IntermediateLookupTest()
{
var pageInfos = new Dictionary<string, string>
{
{ "Home", "home.html" },
{ "About", "about.html" },
{ "Fineprint", "fineprint.html" },
{ "Finish", "finish.html" },
{ "Above", "above.html" }
};
// Corresponds to OP: plsBase = (Lookup<String, pages>)(Query<pages>($@"Select ...").ToLookup(s => s.ip, o => o));
Lookup<string, string> plsBase = (Lookup<string, string>)pageInfos.ToLookup(k => k.Key, v => v.Value);
Lookup<string, string> intermediateLookup = (Lookup<string, string>)pageInfos.ToLookup(k => k.Key.Substring(0, 3), v => v.Key);
var classBIp = "Abo";
var result = new List<string>();
foreach (var plsBaseKey in intermediateLookup[classBIp])
{
result.AddRange(plsBase[plsBaseKey]);
}
Assert.AreEqual(2, result.Count);
Assert.True(result.Contains("about.html"));
Assert.True(result.Contains("above.html"));
}
}
}
选项 2:比较子字符串
var bipLength = classBip.Length;
var pls = plsBase.Where(x =>
(x.Key
.Substring(0, bipLength)
.Equals(classBIp, StringComparison.Ordinal)))
.SelectMany(x => x)
.ToList();
您可能需要对这两个选项进行计时,看看哪一个效果更好。
关于c# - 使用 StartsWith() 时如何提高查找性能,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/61073644/