如何在Erlang中搜索列表中的项目？

wlwcrazw  于 2022-12-08  发布在  Erlang
关注(0)|答案(8)|浏览(176)

I am writing a cache gen-server for the company Use. I am wondering how to search an item from the list as I want the cost of the search for comparing various data structures in erlang like dict, orddict, List, tuples, tree, queue etc to use for cache program.
Example:

List = [{"A1",["ankit","sush", "Hover", "x4", "a3","nilesh","mike","erlang" | ...]}|...].

Now, I want to search for the Key A1 and search for 'mike' in the list. What is the best way to search the above List.
Please provide some examples. Atleast Pseudo for it.

erlang

8条答案

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7gyucuyw

7gyucuyw1#

为了简化https://stackoverflow.com/a/15587565/56250处的示例：

listFind(Element, List) ->
  lists:member(Element, List).

lists:member可以处理空列表，快速查看源代码（https：//github.com/erlang/otp/blob/07 b8 f441 ca 711 f9812 fad 9 e9115 bab 3c 3aa 92 f79/Erts/emulator/beam/erl_bif_lists. c#L184），可以看出它执行起来很慢。

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sd2nnvve

sd2nnvve2#

谢谢你的回答。我已经写了一个Erlang代码来寻找插入和提取日期到各种数据结构的时间，如LIST，DICT，QUEUE，SET和数据结构的并行Map。只有列表的插入和提取完成，但其余的并行Map插入。我想分享代码和代码的结果。以下是模块测试。erl

-module(test).
-author('ankit@hover.in').
-export ([ 
       %%list
       create_list/1, fetch_list/2, test_list/1, parmap_create_list/1 , ins_list/3, parallel_list/1,
       para_fetch_list/2, pfetch_list/1,

       %%dict
       create_dict/1, fetch_dict/2, test_dict/1, parmap_create_dict/1 , ins_dict/3, parallel_dict/1,

       %queue
       create_q/1, fetch_q/2, test_q/1, parmap_create_q/1, ins_q/3, parallel_q/1,

       %set
       create_set/1, fetch_set/2, test_set/1, parmap_create_set/1 , ins_set/3, parallel_set/1,

       create/1, multi_create/0,
       pcreate/1, parallel_multi_create/0

       %test/1 , multi_test/0 
      ]).

%%creation tests

%% For List
create_list(N) ->
    lists:foldl ( fun(X,Prev) -> Prev ++ [X] end, [] , lists:seq(1,N)).

test_list(N) ->
    {R1,List} = timer:tc(?MODULE, create_list, [N]),
    %%Set = lists:foldl(fun(X,Prev) -> sets:add_element(X,Prev) end,SET, lists:seq(1,N)),
    {R2,_} = timer:tc(?MODULE, fetch_list,[ N, List ]),
    {list,inserT,R1,fetchT,R2}.

%% For Dict
create_dict(N) ->
    lists:foldl( fun(X,Prev)-> dict:append([],X,Prev) end, dict:new(), lists:seq(1,N)).

test_dict(N) ->
    {R1,Dict} = timer:tc(?MODULE, create_dict, [N]),
    %%Set = lists:foldl(fun(X,Prev) -> sets:add_element(X,Prev) end,SET, lists:seq(1,N)),
    {R2,_} = timer:tc(?MODULE, fetch_dict,[ N, Dict ]),
    {dict,inserT,R1,fetchT,R2}.

%% For Queue
create_q(N) ->
    lists:foldl(fun(X,Prev) -> queue:in(X,Prev) end, queue:new() , lists:seq(1,N)).

test_q(N)->
    {R1,Q}  = timer:tc(?MODULE, create_q,[N]),
    %%Q = lists:foldl(fun(X,Prev) -> queue:in(X,Prev) end,Q0, lists:seq(1,N)),
    {R2,_} = timer:tc(?MODULE, fetch_q, [ N,Q ] ),
    {queue,inserT,R1,fetchT,R2}.

%% For Set
create_set(N) ->
    SET = sets:new(),
    lists:foldl(fun(X,Prev) -> sets:add_element(X,Prev) end,SET, lists:seq(1,N)).

test_set(N) ->   
    {R1,Set} = timer:tc(?MODULE, create_set, [N]),
    %%Set = lists:foldl(fun(X,Prev) -> sets:add_element(X,Prev) end,SET, lists:seq(1,N)),
    {R2,_} = timer:tc(?MODULE, fetch_set,[ N, Set ]),
    {set,inserT,R1,fetchT,R2}.

create(N)->
    [   timer:tc(?MODULE, X , [N])  || X <- [ test_list, test_dict, test_q,test_set ] ].

xmulti_create()->
    [ ?MODULE:create(X) || X<- [10,100,1000,10000,100000] ].

multi_create() ->
    InputRange = [10,100,1000,10000,100000],
    lists:map(fun(X) ->
              ?MODULE:create(X)
          end,InputRange).

%%fetching midpoint tests
fetch_q(N,Q)->
    fetch_q(N,Q,100).

fetch_q(N,Q,Find) ->
    F = fun(I) -> queue:out_r(I) end,
    R = lists:foldl( fun(_X,{Bool,PrevQ} ) ->
                 {{value, Ele},QQ} = F(PrevQ),
                 Ret1 = case Ele of 
                       Temp when Temp =:= Find -> 
                       true;
                       _ ->
                       Bool
                   end,
                 Ret2 = QQ, 

                 {Ret1,Ret2}

             end,{false,Q}, 
             lists:seq(1,N)),
    R.

fetch_set(N,Set) ->
    fetch_set(N,Set,100).

fetch_set(_N,Set,Find) ->
    Return = sets:is_element(Find,Set),
    Return.

fetch_list(N,List) ->
    fetch_list(N,List,500).

fetch_list(_N,List,Find) ->
    Ret = lists:foldl(fun(X,Prev) when X =:= Find -> true; 
             (X, Prev) -> Prev 
              end,false,List),
    Ret.

fetch_dict(N,Dict) ->
    {ok,List} = dict:find([],Dict),
    fetch_dict(N,List,500).

fetch_dict(_N,List,Find) ->
    Ret = lists:foldl(fun(X,Prev) when X =:= Find -> true; 
             (X, Prev) -> Prev
              end,false,List),
    Ret.

%% parallel operation

%% Parallel Map for Queue
parallel_q(N) ->
    {R1,Set} = timer:tc(?MODULE, parmap_create_q, [N]),
    {parallel_q,pcreate,R1}.

parmap_create_q(N) ->

    PID = spawn(fun() ->
            ?MODULE:ins_q( queue:new(),0,N) end),
    [PID ! {self(),X} || X <- lists:seq(1,N) ],
    receive
    {ok, Q} ->
        %%io:format("~n Still insertin, Q till now ~p",[Q]),
        ok;
    {done, Q}  ->
        io:format("~n *******DONE*********~n ~p",[Q]);
    _E ->
        io:format("unexpected ~p",[_E])
    end.

ins_q(Q,Ctr, Max) ->    
    receive
    {From, N} ->
        %%io:format("~n insert ~p, ctr ~p, Q ~p ~n",[N,Ctr,Q]),
        NewQ = queue:in( N, Q) ,
        case Ctr
        of Temp when Temp < Max ->
            From ! {ok, NewQ};
        _-> 
            From ! {done, NewQ}
        end,
        ?MODULE:ins_q(NewQ,Ctr+1, Max);
    _E ->
        io:format("unexpected ~p",[_E]),
        ?MODULE:ins_q(Q, Ctr, Max)
    end.

%% Parallel Map for set
parallel_set(N) ->
    {R1,Set} = timer:tc(?MODULE, parmap_create_set, [N]),
    {parallel_set,pcreate,R1}.

parmap_create_set(N) ->

    PID = spawn(fun() ->
            ?MODULE:ins_set( sets:new(),0,N) end),
    [PID ! {self(),X} || X <- lists:seq(1,N) ],
    receive
    {ok, Sets} ->
        %%io:format("~n Still insertin, Sets till now ~p",[Sets]),
        ok;
    {done, Sets}  ->
        io:format("~n *******DONE*********~n ~p",[Sets]);
    _E ->
        io:format("unexpected ~p",[_E])
    end.

ins_set(Sets,Ctr, Max) ->    
    receive
    {From, N} ->
        %%io:format("~n insert ~p, ctr ~p, Sets ~p ~n",[N,Ctr,Sets]),
        NewSets = sets:add_element(N,Sets),

        case Ctr
        of Temp when Temp < Max ->
            From ! {ok, NewSets};
        _-> 
            From ! {done, NewSets}
        end,
        ?MODULE:ins_set(NewSets,Ctr+1, Max);
    _E ->
        io:format("unexpected ~p",[_E]),
        ?MODULE:ins_set(Sets, Ctr, Max)
    end.

%% Parallel Map for dict
parallel_dict(N) ->
    {R1,Set} = timer:tc(?MODULE, parmap_create_dict, [N]),
    {parallel_dict,pcreate,R1}.

parmap_create_dict(N) ->

    PID = spawn(fun() ->
            ?MODULE:ins_dict( dict:new(),0,N) end),
    [PID ! {self(),X} || X <- lists:seq(1,N) ],
    receive
    {ok, Dict} ->
        %%io:format("~n Still insertin, Sets till now ~p",[Dict]),
        ok;
    {done, Dict}  ->
        io:format("~n *******DONE*********~n ~p",[Dict]);
    _E ->
        io:format("unexpected ~p",[_E])
    end.

ins_dict(Dict,Ctr, Max) ->    
    receive
    {From, N} ->
        %%io:format("~n insert ~p, ctr ~p, Dict ~p ~n",[N,Ctr,Dict]),
        NewDict = dict:append([],N,Dict),

        case Ctr
        of Temp when Temp < Max ->
            From ! {ok, NewDict};
        _-> 
            From ! {done, NewDict}
        end,
        ?MODULE:ins_dict(NewDict,Ctr+1, Max);
    _E ->
        io:format("unexpected ~p",[_E]),
        ?MODULE:ins_dict(Dict, Ctr, Max)
    end.

%% Parallel Map for list
parallel_list(N) ->
    {R1,List} = timer:tc(?MODULE, parmap_create_list, [N]),
    {R2,_} = timer:tc(?MODULE, para_fetch_list, [N,List]),
    {parallel_list,pCreate,R1,pFetch,R2}.

parmap_create_list(N) ->

    PID = spawn(fun() ->
            ?MODULE:ins_list( [],0,N) end),
    [PID ! {self(),X} || X <- lists:seq(1,N) ],
    receive
    {ok, List} ->
        %%io:format("~n Still insertin, List till now ~p",[List]),
        ok;
    {done, List}  ->
        io:format("~n *******DONE*********~n ~p",[List]);
    _E ->
        io:format("unexpected ~p",[_E])
    end.

ins_list(List,Ctr, Max) ->    
    receive
    {From, N} ->
        %%io:format("~n insert ~p, ctr ~p, Sets ~p ~n",[N,Ctr,Dict]),
        NewList = List ++ [N] ,

        case Ctr
        of Temp when Temp < Max ->
            From ! {ok, NewList};
        _-> 
            From ! {done, NewList}
        end,
        ?MODULE:ins_list(NewList,Ctr+1, Max);
    _E ->
        io:format("unexpected ~p",[_E]),
        ?MODULE:ins_list(List, Ctr, Max)
    end.

para_fetch_list(List, FindN) ->
    Pid = spawn(fun() ->
            ?MODULE:pfetch_list(FindN) end),
    Self = self(),
    Now1 = now(),
    lists:map ( fun(X) ->
            Pid ! {Self, X},
            receive
                {true,Find} ->
                io:format("~n Found ~p ",[Find]),
                true;
                {false,Find}  ->
                %io:format("~n NOT FOUND ~p ",[Find]),
                false;
                _E ->
                io:format("para main unexpected ~p",[_E])
            after 4000 ->
                io:format("timerout ",[])

            end
        end, List ) ,
    Now2 = now(),
    timer:now_diff(Now2,Now1).

pfetch_list(Find) ->    
    receive
    {From, CurrN} ->

        _Ret = case CurrN of 
              Temp when Temp =:= Find ->
              From ! {true,Find},
              true;
              _ -> 
              From ! {false,Find},
              false
          end,
        %%io:format("~n insert ~p, ctr ~p, Sets ~p ~n",[N,Ctr,Dict]),
        ?MODULE:pfetch_list(Find);
    _E ->
        io:format("pfetch unexpected ~p",[_E]),
        ?MODULE:pfetch_list(Find)
    end.    

pcreate(N)->
    [   timer:tc(?MODULE, X , [N])  || X <- [ parallel_list ] ].

parallel_multi_create() ->
    InputRange = [10,100,1000,10000],
    lists:map(fun(X) ->
              ?MODULE:pcreate(X)
          end,InputRange).

**结果如下：**对于并行Map DS

(ankit@127.0.0.1)2> test:pcreate(1000).
[{5399,{parallel_list,pCreate,5352,pFetch,30}},
 {9886,{parallel_dict,pcreate,9875}},
 {87603,{parallel_q,pcreate,87593}},
 {42271,{parallel_set,pcreate,42223}}]

对于所有DS

(ankit@127.0.0.1)3> test:multi_create().
 %% For 10   
[[{38,{list,inserT,14,fetchT,8}},
      {91,{dict,inserT,67,fetchT,11}},
      {47,{queue,inserT,13,fetchT,21}},
      {81,{set,inserT,61,fetchT,7}}],
%%for 100
     [{234,{list,inserT,191,fetchT,30}},
      {690,{dict,inserT,642,fetchT,35}},
      {218,{queue,inserT,60,fetchT,144}},
      {559,{set,inserT,540,fetchT,6}}],
%% for 1000
     [{13746,{list,inserT,13452,fetchT,262}},
      {96137,{dict,inserT,96009,fetchT,116}},
      {967,{queue,inserT,284,fetchT,674}},
      {5562,{set,inserT,5547,fetchT,5}}],
%% for 10000  
   [{438301,{list,inserT,437256,fetchT,1027}},
      {361450,{dict,inserT,360412,fetchT,1020}},
      {7937,{queue,inserT,2292,fetchT,5636}},
      {31293,{set,inserT,31279,fetchT,5}}],
% for 100000
     [{43750210,{list,inserT,43739956,fetchT,10238}},
      {51517971,{dict,inserT,51507134,fetchT,10819}},
      {92503,{queue,inserT,29676,fetchT,62811}},
      {682118,{set,inserT,682100,fetchT,5}}]]

希望这些信息能帮助你确定哪一个是最好的DS用于不同的目的。我会更新它时，我完成了整个代码。

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chhqkbe1

chhqkbe13#

如果您想搜索列表，请使用list module中的函数，它是Erlang附带的extensive documentation的一部分。
如果你想知道最好的数据结构使用-这是一个稍微不同的问题，将需要更多的信息。

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7ivaypg9

7ivaypg94#

使用lists模块中的keyfind函数。例如：

30> List = [{"A1",["ankit","sush", "Hover", "x4", "a3","nilesh","mike","erlang"]}].
[{"A1",
  ["ankit","sush","Hover","x4","a3","nilesh","mike",
   "erlang"]}]
31> lists:keyfind("A1", 1, List).
{"A1",
 ["ankit","sush","Hover","x4","a3","nilesh","mike","erlang"]}
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crcmnpdw

crcmnpdw5#

如果你想要这种“列表”，你可以很容易地手工制作自己的搜索：

search_key(Key, [{Key,_}=V|_]) -> {ok, V};
search_key(Key, [_|T]) -> search_key(Key, T);
search_key(_, []) -> not_found.

search_val(Val, [{_,L}=X|T]) ->
  case _search_val(Val, L) of
    ok -> {ok, X};
    not_found -> search_val(Val, T)
  end;
search_val(_, []) -> not_found.

_search_val(Val, [Val|_])-> ok;
_search_val(Val, [_|T])-> _search_val(Val, T);
_search_val(_,[])-> not_found.

但我不确定你到底想要什么。例如，如果你想在列表中搜索键“A1”，而不是值“mike”，这将是不同的解决方案。如果你想知道如何以最佳结构存储这种排序，这只是另一个问题。你应该提供更多的信息。

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uujelgoq

uujelgoq6#

如果您的列表是一个简单的基于一个字词的项目列表，那么最简单的解决方案是：

listFind ( Element, [] ) ->
    false;

listFind ( Element, [ Item | ListTail ] ) ->
    case ( Item == Element ) of
        true    ->  true;
        false   ->  listFind(Element, ListTail)
    end.

上面的操作假设您使用**==**运算符检查列表中的项目是否相等。您可以根据需要修改该运算符以适应其他类型的比较/相等。

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gmol1639

gmol16397#

You can also use any from http://erlang.org/doc/man/lists.html#any-2

lists:any(fun(X) -> X == <<"yourthing">> end, YourList)

如果找到，将传回true，否则传回false。

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hmmo2u0o

hmmo2u0o8#

再简单不过了：

fein(_, []) ->
    [];
fein(Element, [Item| ListTail]) ->
    case (Item =:= Element) of
    true -> [Element|fein(Element, ListTail)];
    false -> fein(Element, ListTail)
    end.
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