How to optimize the speed of list traversal in C #

A database table (id, name ,...) There are 0.1 million records. It may take a long time to search for name = 'guoguo'. However, if you create an index for the name, then, query with name = 'guoguo' will become very fast (how fast? You can try it yourself ).

Correspondingly, sometimes our code uses List <T> and Array to store a group of data. Let's take an example.

Define the Data Type:

       ID { ;   Name { ;   Age { ; 

. You can use the following code to find the corresponding UserInfo from the List by name:

        List<UserInfo> UserInfo GetUserInfoByName( ( i = ; i < _userinfos.Count; i++= (ui.Name ==  UserInfo GetUserInfoByName_Find( _userinfos.Find((temp) => temp.Name ==

Both methods are compared and searched by traversing the list. I did an experiment. If the list contains 0.1 million records, it takes 5th times to search for 1000 million elements respectively:

GetUserInfoByName	1877 Ms
GetUserInfoByName_Find	2290 Ms

That is to say, the average time is about 2 milliseconds (the Find efficiency is lower );

OK. Next we will try to create an index for the List using the database method.

         List<UserInfo> { =<, UserInfo>                   <, UserInfo> userIndex =  Dictionary<, UserInfo> ( item =

The MakeIndex method is called in the set attribute of Userinfos. The query method should be written as follows:

         UserInfo GetUserInfoByNameEx(

So simple? Yes, it is so simple and efficient. Compare with the preceding two methods:

Index creation + SEARCH 0.1 million times = 36 ms!

The reason is that the time complexity of the Dictionary [Key] method is O (1), which is almost time-consuming.

All the sample code is as follows:

Main (<UserInfo> userinfos = List <UserInfo> (I =; I <*; I ++ ====. format (nameToFind = userinfos [* (I =; I <; I ++. format (I =; I <; I ++. format (I =; I <*; I ++. format (<UserInfo> List <UserInfo >{= <, UserInfo> UserInfo GetUserInfoByName (I =; I <_ userinfos. count; I ++ = (ui. name = UserInfo GetUserInfoByName_Find (_ userinfos. find (temp) => temp. name = <, UserInfo> userIndex = Dictionary <, UserInfo> (item = UserInfo GetUserInfoByNameEx (ID {; Name {; Age {;Sample Code