orddict 是用List实现的有序Dictionary. orddict按照Key进行排序,

Key值不重复(对比一下proplists).每一次增加新数据项都会进行重新排序,所以通常情况查找会非常快.由于也是List和tuple实现,所以和proplists一样orddict也不适合大数据量的情况.注意orddict进行Key比较使用的是相等(==).通过模块暴露出来的接口完成对orddict的处理,不要当作普通的list直接处理,因为一些操作会涉及到重排序.

LYSE上提到orddict在复杂性和效率上达到折中,元素最好不要超过

75个.

Orddicts are a generally good compromise between complexity and efficiency up to about 75 elements (see ). After that amount, you should switch to different key-value stores.

Link:

由于orddict实际上就是一个List的实现,相比proplists它的实现要简单很多.大多数方法都是下面逻辑的微调:

store(Key, New, [{K,_}=E|Dict]) when Key < K ->    [{Key,New},E|Dict];store(Key, New, [{K,_}=E|Dict]) when Key > K ->    [E|store(Key, New, Dict)];store(Key, New, [{_K,_Old}|Dict]) ->          %Key == K    [{Key,New}|Dict];         store(Key, New, []) -> [{Key,New}].

比如:

append(Key, New, [{K,_}=E|Dict]) when Key < K ->    [{Key,[New]},E|Dict];append(Key, New, [{K,_}=E|Dict]) when Key > K ->    [E|append(Key, New, Dict)];append(Key, New, [{_K,Old}|Dict]) ->          %Key == K    [{Key,Old ++ [New]}|Dict];append(Key, New, []) -> [{Key,[New]}].

再比如:

append_list(Key, NewList, [{K,_}=E|Dict]) when Key < K ->    [{Key,NewList},E|Dict];append_list(Key, NewList, [{K,_}=E|Dict]) when Key > K ->    [E|append_list(Key, NewList, Dict)];append_list(Key, NewList, [{_K,Old}|Dict]) ->          %Key == K    [{Key,Old ++ NewList}|Dict];append_list(Key, NewList, []) ->    [{Key,NewList}].

Practice

Eshell V5.9.1  (abort with ^G)1>  D0 = orddict:new().[]2>  D1 = orddict:store(files, [], D0),  D2 = orddict:append(files, f1, D1),  D3 = orddict:append(files, f2, D2),  D4 = orddict:append(files, f3, D3),  orddict:fetch(files, D4).[f1,f2,f3]3> b().D0 = []D1 = [{files,[]}]D2 = [{files,[f1]}]D3 = [{files,[f1,f2]}]D4 = [{files,[f1,f2,f3]}]ok4>   D5 = orddict:append(dirs, dd, D4),D5.[{dirs,[dd]},{files,[f1,f2,f3]}]5>   D6 = orddict:append(a, abc, D5).[{a,[abc]},{dirs,[dd]},{files,[f1,f2,f3]}]6>   D7 = orddict:append(z, abc, D6).[{a,[abc]},{dirs,[dd]},{files,[f1,f2,f3]},{z,[abc]}]7> orddict:fetch_keys(D7).[a,dirs,files,z]8> orddict:fetch(a,D7).[abc]9> orddict:fetch(files,D7).[f1,f2,f3]   10> D7.[{a,[abc]},{dirs,[dd]},{files,[f1,f2,f3]},{z,[abc]}]11> orddict:append(z, qqq, D7).[{a,[abc]},{dirs,[dd]},{files,[f1,f2,f3]},{z,[abc,qqq]}]12> orddict:store(z, qqq, D7).[{a,[abc]},{dirs,[dd]},{files,[f1,f2,f3]},{z,qqq}]13>   orddict:store17> D7.[{a,[abc]},{dirs,[dd]},{files,[f1,f2,f3]},{z,[abc]}]18> orddict:store(k,lala, D7).[{a,[abc]},{dirs,[dd]},{files,[f1,f2,f3]},{k,lala},{z,[abc]}]20> orddict:append_list(k, [qqq], v(18)).** exception error: bad argument     in operator  ++/2        called as lala ++ [qqq]     in call from orddict:append_list/3     in call from orddict:append_list/321> orddict:append_list(k, qqq, v(18)).** exception error: bad argument     in operator  ++/2        called as lala ++ qqq     in call from orddict:append_list/3     in call from orddict:append_list/322>  orddict:erase22> D7.[{a,[abc]},{dirs,[dd]},{files,[f1,f2,f3]},{z,[abc]}]23> orddict:erase(a,D7).[{dirs,[dd]},{files,[f1,f2,f3]},{z,[abc]}]24>  orddict:filterfilter(Pred, Orddict1) -> Orddict2Pred = fun(Key, Value) -> bool() 28> orddict:filter(fun(K,N)->is_list(N) andalso length(N) >1 end ,D7).[{files,[f1,f2,f3]}]29>  orddict:foldfold(Fun, Acc0, Orddict) -> Acc1Fun = fun(Key, Value, AccIn) -> AccOut29> orddict:fold(fun(K,V,N)-> length(V)+N end ,0,D7).630> orddict:from_listfrom_list(List) -> OrddictList = [{Key, Value}]注意:重复数据项出现的时候,会采用最后出现的Value值30> orddict:from_list([{a,1},{b,2},{c,3}]).[{a,1},{b,2},{c,3}]31> orddict:from_list([{z,1},{b,2},{c,3}]).[{b,2},{c,3},{z,1}]32> orddict:from_list([{
   "zen",1},{b,2},{c,3}]).[{b,2},{c,3},{
   "zen",1}]33> orddict:from_list([{
   "zen",1},{b,2},{c,3},{
   1.0,p},{
   1,q}]).[{
    1,q},{b,2},{c,3},{
   "zen",1}]34> orddict:is_key34> orddict:is_key(z,D7).true35> orddict:is_key(p,D7).false36> orddict:mapmap(Fun, Orddict1) -> Orddict2Fun = fun(Key, Value1) -> Value2 36> orddict:map(fun(K,V)->{K,{K,V,term_to_binary(V)}} end ,D7).[{a,{a,{a,[abc],<<131,108,0,0,0,1,100,0,3,97,98,99,106>>}}},{dirs,{dirs,{dirs,[dd],                   <<131,108,0,0,0,1,100,0,2,100,100,106>>}}},{files,{files,{files,[f1,f2,f3],                      <<131,108,0,0,0,3,100,0,2,102,49,100,0,2,102,50,100,0,                        2,...>>}}},{z,{z,{z,[abc],<<131,108,0,0,0,1,100,0,3,97,98,99,106>>}}}]37>  orddict:update38> orddict:update(a,fun(V)-> term_to_binary(V) end,D7).[{a,<<131,108,0,0,0,1,100,0,3,97,98,99,106>>},{dirs,[dd]},{files,[f1,f2,f3]},{z,[abc]}]39> orddict:update(dvd,fun(V)-> term_to_binary(V) end,D7).** exception error: no function clause matching                    orddict:update(dvd,#Fun
     
      ,                                   [{files,[f1,f2,f3]},{z,[abc]}])     in function  orddict:update/340> orddict:update(dvd,fun(V)-> term_to_binary(V) end,not_found,D7).[{a,[abc]},{dirs,[dd]},{dvd,not_found},{files,[f1,f2,f3]},{z,[abc]}]41>  orddict:update_counterupdate_counter(Key, Incr, D) ->    update(Key, fun (Old) -> Old + Incr end, Incr, D). 47> orddict:update_counter(a,1,[{a,10},{b,13},{c,16}]).[{a,11},{b,13},{c,16}]48>

晚安!