erlang random sort

a.单进程10万次随机3个元素.

[{"192.168.17.102",27017},    {"192.168.17.102",27018},    {"192.168.17.102",27019}]

b.随机10个元素

[1,2,3,4,5,6,7,8,9,10]

c.随机100个元素

lists:seq(1, 100).

1.https://erlangcentral.org/wiki/index.php/RandomShuffle

We associate each element in the list with a random number. The list is then sorted based on the generated number.We repeat this process log(n) times to ensure a fair shuffle.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% shuffle(List1) -> List2%% Takes a list and randomly shuffles it. Relies on random:uniform%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% shuffle(List) ->%% Determine the log n portion then randomize the list.   randomize(round(math:log(length(List)) + 0.5), List). randomize(1, List) ->   randomize(List);randomize(T, List) ->   lists:foldl(fun(_E, Acc) ->                  randomize(Acc)               end, randomize(List), lists:seq(1, (T - 1))). randomize(List) ->   D = lists:map(fun(A) ->                    {random:uniform(), A}             end, List),   {_, D1} = lists:unzip(lists:keysort(1, D)),   D1.

a.350～370ms  b.1600ms c.26800ms

2.

rotate_new(RotatedList, [L]) ->[L | RotatedList];rotate_new(RotatedList, List) ->R = random:uniform(length(List)),L = lists:nth(R, List),rotate_new([L | RotatedList], List--[L]).

a.90ms b.410ms c.13550ms

3. http://stackoverflow.com/questions/8817171/shuffling-elements-in-a-list-randomly-re-arrange-list-elements

1> L = lists:seq(1,10).[1,2,3,4,5,6,7,8,9,10]

Associate a random number R with each element X in L by making a list of tuples {R, X}. Sort this list and unpack the tuples to get a shuffled version of L.

1> [X||{_,X} <- lists:sort([ {random:uniform(), N} || N <- L])].[1,6,2,10,5,7,9,3,8,4]2>     

a.120ms  b.420ms c.5100ms

4. http://stackoverflow.com/questions/8817171/shuffling-elements-in-a-list-randomly-re-arrange-list-elements

list([])     -> [];list([Elem]) -> [Elem];list(List)   -> list(List, length(List), []).list([], 0, Result) ->    Result;list(List, Len, Result) ->    {Elem, Rest} = nth_rest(random:uniform(Len), List),    list(Rest, Len - 1, [Elem|Result]).nth_rest(N, List) -> nth_rest(N, List, []).nth_rest(1, [E|List], Prefix) -> {E, Prefix ++ List};nth_rest(N, [E|List], Prefix) -> nth_rest(N - 1, List, [E|Prefix]).

For example, one could probably do away with the ++ operation in nth_rest/3. You don't need to seed the random algorithm in every call to random. Seed it initially when you start your program, like so: random:seed(now()). If you seed it for every call touniform/1 your results become skewed (try with [shuffle:list([1,2,3]) || _ <- lists:seq(1, 100)]).

a.130ms  b.410ms c.8500ms

5.

shuffle(L) ->    shuffle(list_to_tuple(L), length(L)).shuffle(T, 0)->    tuple_to_list(T);shuffle(T, Len)->Rand = random:uniform(Len),A = element(Len, T),B = element(Rand, T),T1 = setelement(Len, T,  B),T2 = setelement(Rand,  T1, A),shuffle(T2, Len - 1).

a.130ms  b.390ms c.5850