[集]erlang常用函数收集

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]

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]