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lists模块

duplicate/2

结构:

duplicate(N, Elem) -> List
类型
N = integer() >= 0
Elem = T
List = [T]
T = term()

说明:

Returns a list containing N copies of term Elem.

实例:

> lists:duplicate(5, xx).
[xx,xx,xx,xx,xx]

filter/2

用法:

filter(Pred, List1) -> List2
类型
Pred = fun((Elem :: T) -> boolean())
List1 = List2 = [T]
T = term()

说明:

List2是List1中的元素在执行Pred(Elem)函数时返回true的列表

filtermap/2

用法:

filtermap(Fun, List1) -> List2
类型:
Fun = fun((Elem) -> boolean()| {true, Value})
List1 = [Elem]
List2 = [Elem | Value]

说明:

按函数Fun进行过滤

代码展示实现功能:

filtermap(Fun, List1) ->
  lists:foldr(
    fun(Elem, Acc) ->
       case Fun(Elem) of
           false -> Acc;
           true -> [Elem|Acc];
           {true,Value} -> [Value|Acc]
       end
    end, [], List1).

实例:

> lists:filtermap(
  fun(X) ->
    case X rem 2 of
      0 -> {true, X div 2};
      _ -> false
    end
  end, [1,2,3,4,5]).
结果:[1,2]

foreach/2

用法:

foreach(Fun, List) -> ok
类型:
Fun = fun((Elem :: T) -> term())
List = [T]
T = term()

说明:

对List中的每个元素调用Fun(Elem)
得到的结果顺序与List顺序相同

实例:

L1 = [1,2,3,4,5].
lists:foreach(fun(X) -> io:format("~p~n", [X]) end, L1).

L2 = [{a1, b1}, {a2, b2}, {a3, b3}].
Fun = fun({A, _}) ->
    io:format("~p~n", [A])
end.
lists:foreach(Fun, L2).

foldl/3

用法:

foldl(Fun, Acc0, List) -> Acc1
类型:
Fun = fun((Elem :: T, AccIn) -> AccOut)
Acc0 = Acc1 = AccIn = AccOut = term()
List = [T]
T = term()

解释:

遍历List, 一次次执行Fun/2函数,
Fun/2函数:
第1个参数是List中的每次的值,
第2个参数初使值为Acc0, 之后每次是前一次的结果

实例:

> lists:foldl(fun(X, Sum) -> X + Sum end, 0, [1,2,3,4,5]).
15
> lists:foldl(fun(X, Prod) -> X * Prod end, 1, [1,2,3,4,5]).
120

keyfind/3

用法:

keyfind(Key, N, TupleList) -> Tuple | false
类型:
Key = term()
N = integer() >= 1
1..tuple_size(Tuple)
TupleList = [Tuple]
Tuple = tuple()

解释:

取出指定key对应的tuple

实例:

> lists:keyfind(a, 1, [{a,1}, {b,2}]).
{a, 1}
> lists:keyfind(a, 1, [{ad,1}, {b,2}, {a,a,b}]).
{a, a, b}

keymember/3

用法:

keyfind(Key, N, TupleList) -> true | false
类型:
Key = term()
N = integer() >= 1
1..tuple_size(Tuple)
TupleList = [Tuple]
Tuple = tuple()

解释:

查询tuple列表TupleList，并把它的第N个元素与Key对比是否相同
如果相同返回true，否则返回false

实例:

lists:keymember(octopus, 1, application:which_applications()).

keyreplace/4

用法:

keyreplace(Key, N, TupleList1, NewTuple) -> TupleList2
类型:
Key = term()
N = integer() >= 1; 1..tuple_size(Tuple)
TupleList1 = TupleList2 = [Tuple]
NewTuple = Tuple
Tuple = tuple()

说明:

如果TupleList1中的tuple的第N位的值等于Key,则把此tuple的值替换为NewTuple

实例:

%% 示例
lists:keyreplace(env, 1, AppSpec, {env, Env}).
%% 实例
1> List = [{key1, value1}, {key2, value2}].
[{key1,value1},{key2,value2}]
2> lists:keyreplace(key1, 1, List, {key1, abc}).
[{key1,abc},{key2,value2}]

keysort/2

用法:

keysort(N, TupleList1) -> TupleList2
类型:
N = integer() >= 1
TupleList1 = TupleList2 = [Tuple]

说明:

Returns a list containing the sorted elements of list TupleList1. Sorting is performed on the Nth element of the tuples. The sort is stable.

keytake/3

用法:

keytake(Key, N, TupleList1) -> {value, Tuple, TupleList2} | false

说明:

把TupleList1中第N列与Key对比,如果都不相同返回false,
如果相同, Tuple即为第1个与Key相同的值, TupleList2是去除了Tuple后的tuple列表

实例:

> lists:keytake(a, 1, [{ad,1}, {b,2}, {a,a,b}]).
{value,{a,a,b},[{ad,1},{b,2}]}

member/2

用法:

member(Elem, List) -> boolean()
类型:
Elem = T
List = [T]
T = term()

解释:

如果列表List中有Elem返回true，否则返回true

实例:

1> List = [1,2,3,4,5].
[1,2,3,4,5]
2> lists:member(3, List).
true

partition/2

用法:

partition(Pred, List) -> {Satisfying, NotSatisfying}
类型:
Pred = fun((Elem :: T) -> boolean())
List = Satisfying = NotSatisfying = [T]
T = term()

说明:

对列表进行区分,Pred函数执行为true的归类到Satisfying,其他的归类到NotSatisfying

实例:

> lists:partition(fun(A) -> A rem 2 == 1 end, [1,2,3,4,5,6,7]).
{[1,3,5,7],[2,4,6]}
> lists:partition(fun(A) -> is_atom(A) end, [a,b,1,c,d,2,3,4,e]).
{[a,b,c,d,e],[1,2,3,4]}

排序相关

sort/1

sort(List1) -> List2
类型:
List1 = List2 = [T]
T = term()

说明:

Returns a list containing the sorted elements of List1.

sort/2

sort(Fun, List1) -> List2
类型:
Fun = fun((A :: T, B :: T) -> boolean())
List1 = List2 = [T]
T = term()

说明:

基于排序函数Fun, 返回排序的列表List1
函数Fun(A, B): 如果A<=B, 则返回true; 反之返回false

实例1:

% 最简单实例
Fun = fun(A, B) ->
  A =< B
end.
List = [1, 3, 5, 2, 6, 4].
lists:sort(Fun, List).

实例2:

% 取出所有进程reductions最高的前5个进程
Fun = fun({reductions,R1}, {reductions,R2}) ->
  R1 > R2
end.
List = [process_info(Pid, reductions) || Pid <- processes()].
lists:sublist(lists:sort(Fun, List), 5).

实例3:

% 列表中列表
Fun = fun(List1, List2) ->
  {reductions,R1} = lists:nth(1, List1),
  {reductions,R2} = lists:nth(1, List2),
  R1 > R2
end.
List = [process_info(Pid, [reductions, registered_name]) || Pid <- processes()].
lists:sublist(lists:sort(Fun, List), 5).

split/2

split(N, List1) -> {List2, List3}

类型:
N = integer() >= 0
    0..length(List1)
List1 = List2 = List3 = [T]
T = term()

说明:

拆分List1,拆分后
List2包含前N个元素
List3包含剩下的元素

prefix/2

prefix(List1, List2) -> boolean()
类型
List1 = List2 = [T]
T = term()
如果List1是List2的prefix返回true，否则返回false

实例:

14 > lists:prefix([], []).
true
15> lists:prefix([abc], [abc, def]).
true
16> lists:prefix([abc], [abcdef]).
false

zip/2

结构:

zip(List1, List2) -> List3
Types
List1 = [A]
List2 = [B]
List3 = [{A, B}]
A = B = term()

说明:

把两个长度相同的列表List1, List2合并成一个两元素tuple的新列表的List3

实例:

$> List1 = [a, b, c].
$> List2 = [1, 2, 3].
$> lists:zip(List1, List2).
[{a,1},{b,2},{c,3}]

zip3/3

结构:

zip3(List1, List2, List3) -> List4
Types
List1 = [A]
List2 = [B]
List3 = [C]
List4 = [{A, B, C}]
A = B = C = term()

说明:

参见zip/2

实例:

$> List3 = ['!', '@', '#'].
$> lists:zip3(List1, List2, List3).
[{a,1,'!'},{b,2,'@'},{c,3,'#'}]

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