我正在为公司使用编写缓存gen-server。我想知道如何从列表中搜索项目，因为我希望搜索比较各种数据结构的搜索成本，如dict，orddict，List，元组，树，队列等用于缓存程序。
示例：
List = [{"A1",["ankit","sush", "Hover", "x4", "a3","nilesh","mike","erlang" | ...]}|...].
现在，我想搜索Key A1并在列表中搜索“mike”。搜索上面列表的最佳方法是什么。
请提供一些例子。 Atleast Pseudo for it。
答案 0 :(得分：7)
只是为了简化https://stackoverflow.com/a/15587565/56250上的示例：
listFind(Element, List) ->
lists:member(Element, List).
lists:member适用于空列表。快速查看源代码（https://github.com/erlang/otp/blob/07b8f441ca711f9812fad9e9115bab3c3aa92f79/erts/emulator/beam/erl_bif_lists.c#L184）表明它执行得很懒散。
答案 1 :(得分：4)
感谢您的回答。 我写了一个Erlang代码来查找Inserting＆amp; amp;的时间。将日期提取到各种数据结构中，如数据结构的 LIST，DICT，QUEUE，SET和PARALLEL MAP 。只有列表的插入＆amp; fetch完成但是rest有并行映射插入。我想分享一下代码＆amp;代码的结果。以下是模块test.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).
以下是结果： 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}}]
适用于所有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}}]]
希望这些信息可以帮助您确定哪个DS是用于不同目的的最佳DS。当我完成整个代码时，我会更新它。
答案 2 :(得分：3)
如果要搜索列表，请使用list module中的函数，该函数是Erlang附带的extensive documentation的一部分。
如果您想知道要使用的最佳数据结构 - 这是一个稍微不同的问题，需要更多信息。
答案 3 :(得分：3)
使用keyfind模块中的lists功能。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"]}
答案 4 :(得分：2)
如果您想要这种“列表”，您可以轻松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，如果要在列表中搜索键“A1”而不是值“mike”，则它将是不同的解决方案。如果你想知道如何在最佳结构中存储这种类型，那只是另一个问题。您应该提供更多信息。
答案 5 :(得分：1)
如果您的列表是一个简单的基于术语的项目列表，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.
如果您使用 == 运算符检查列表中项目的相等性，则上述方法可行。您可以根据需要修改该运算符以容纳其他类型的比较/相等。
答案 6 :(得分：1)
您还可以使用http://erlang.org/doc/man/lists.html#any-2
中的any
lists:any(fun(X) -> X == <<"yourthing">> end, YourList)
如果找到则返回true，否则返回false。