erlang 函数

1、消重算法：

1> List = [1,2,3,1,2,4]. 

[1,2,3,1,2,4] 

2> sets:to_list(sets:from_list(List)). 

[3,2,1,4]

2、排序算法：
3>lists:sort(List). 

[1,1,2,2,3,4]
根据某一元素排序
4>rd(app{id,date,pkg_name,appname,version,user_num,new_user_num,used_num,los,sum_user}). 

app 

5> Sort = fun (A,B)-> A#app.date =< B#app.date end.                             

#Fun<erl_eval.12.113037538> 

6> lists:sort(Sort, D).%按记录中的date字段进行排列 

[#app{                         

      id = {app_id,{2010,7,1},<<"Packagename">>}, 

      date = {2010,7,1}, 

      pkg_name = <<"Packagename">>,appname = <<"Appname">>, 

      version = <<"Version">>,user_num = 1,new_user_num = 1, 

      used_num = 1,los = 7223,sum_user = 2}... ...


3、排序+消重算法：
7> ordsets:from_list(List). 

[1,2,3,4]

foldl(Fun(Elem, AccIn), Acc0, List) -> Acc1　　%%AccIn初使为Acc0, Elem是List中的值，把List中的所有值都执行函数一次得到列表 

　　lists:foldl(fun(Key, Acc) ->[proplists:get_value(Key, Options) | Acc]  end,  [], lists:reverse([pool_id, hostname, port, username,password,database, logfun, encoding, poolsize])) 

注：这儿的Options="[{hostname,"localhost"}, {username, "root"}, {password,"sa"}, {database, "test"}]"

结果为[undefine,"localhost", undefine,"root","sa","test", undefine, undefine, undefine]

4.whereis ,检测进程是否存在。
5.process_flag(trap_exit, true)来将一个正常的进程转换为一个可以trap exits的系统进程.