【C#】 Array / List / Dictionary之相互转换，从List中获取指定元素 各方式效率对比

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Array / List / Dictionary之相互转换

声明测试数据：

string[] testAarray = new string[] ｛ "array01", "array02", "array03", "array04", "array05" ｝;
List<string> testList = new List<string>() ｛ "list01", "list02", "list03", "list04", "list05" ｝;
Dictionary<int, string> testDic = new Dictionary<int, string>() ｛ ｛ 1, "dictionary01" ｝, ｛ 2, "dictionary02" ｝, ｛ 3, "dictionary03" ｝ ｝;

---

Array数组的 复制、转List、转Dictionary：

• Array复制 目标数组.CopyTo(接收数组, 复制起点)

string[] copyArray = new string[5];
testAarray.CopyTo(copyArray, 0);

• Array转List

List<string> arrayToList = new List<string>(testAarray);

• Array转Dictionary 引入命名空间using System.Linq;Array下标作为Dictionary的key，元素作为value，利用lambda转换

Dictionary<int, string> arrayToDic = testAarray.ToDictionary(arrayItem => System.Array.IndexOf(testAarray, arrayItem), arrayItem => arrayItem);

---

List列表的 复制、转Array、转Dictionary：

• List复制

List<string> copyList = new List<string>(testList);

• List转Array List.ToArray()，或者，List复制到Array，与Aarray.CopyTo相同，调用List.ToArray()

string[] listToArray = testList.ToArray();
//或
string[] listCopyToArray = new string[5];
testList.CopyTo(listCopyToArray, 0);

• List转Dictionary 与Array转Dictionary相同

Dictionary<int, string> listToDic = testList.ToDictionary(listItem => testList.IndexOf(listItem), listItem => listItem);

---

Dictionary字典的 复制、转Array、转List：

• //Dictionary复制

Dictionary<int, string> copyDic = new Dictionary<int, string>(testDic);

• Dictionary转Array

int[] dictionaryKeyToArray = testDic.Keys.ToArray<int>();
string[] dictionaryToArray = testDic.Values.ToArray<string>();

• Dictionary转List

List<int> dictionaryKeyToList = testDic.Keys.ToList<int>();
List<string> dictionaryToList = testDic.Values.ToList<string>();

---

# 判断某元素是否在List内、从List中获取指定元素 各方式效率对比

判断或获取方式：# List.Exists、List.Contains、List.Find、Linq

测试代码：

        List<int> testList = new List<int>();
        for(int i = 0; i < 10000; i++)
        {
            testList.Add(i);
        }
 
        DateTime startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            if(testList.Contains(i))
            { }
        }
        Debug.Log(DateTime.Now - startTime + " : Contains");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            if(testList.Exists(item => item == i))
            { }
        }
        Debug.Log(DateTime.Now - startTime + " : Exists");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            if(testList.Any(item => item == i))
            { }
        }
        Debug.Log(DateTime.Now - startTime + " : Any");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            testList.FirstOrDefault(item => item == i);
        }
        Debug.Log(DateTime.Now - startTime + " : First");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            testList.Where(item => item == i).FirstOrDefault();
        }
        Debug.Log(DateTime.Now - startTime + " : Where");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            testList.Find(item => item == i);
        }
        Debug.Log(DateTime.Now - startTime + " : Find");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            for(int j = 0; j < testList.Count; j++)
            {
                if(i == testList[j])
                    break;
            }
        }
        Debug.Log(DateTime.Now - startTime + " : For");

测试结果：

用List再测一下：

        List<string> testList = new List<string>();
        for(int i = 0; i < 10000; i++)
        {
            testList.Add(i.ToString());
        }
 
        DateTime startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            if(testList.Contains("5000"))
            { }
        }
        Debug.Log(DateTime.Now - startTime + " : Contains");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            if(testList.Exists(item => item == "5000"))
            { }
        }
        Debug.Log(DateTime.Now - startTime + " : Exists");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            if(testList.Any(item => item == "5000"))
            { }
        }
        Debug.Log(DateTime.Now - startTime + " : Any");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            testList.FirstOrDefault(item => item == "5000");
        }
        Debug.Log(DateTime.Now - startTime + " : First");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            testList.Where(item => item == "5000").FirstOrDefault();
        }
        Debug.Log(DateTime.Now - startTime + " : Where");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            testList.Find(item => item == "5000");
        }
        Debug.Log(DateTime.Now - startTime + " : Find");
 
        startTime = DateTime.Now;
        for(int i = 0; i < 20000; i++)
        {
            for(int j = 0; j < testList.Count; j++)
            {
                if("5000" == testList[j])
                    break;
            }
        }
        Debug.Log(DateTime.Now - startTime + " : For");

测试结果：

测试结论：

• 判断某元素是否在List内，List.Exists优于List.Contains；
• 从List中获取指定的元素，List.Find优于Linq，优于For循环。