如何检查元素是否不在列表中，如果不在，则插入 [英] How to check if element is not in a list, if it isn't, insert it

问题描述

我想要，给定一个由 AB 元素 ([ab,bc,cd]) 组成的列表，检查某个给定元素是否已经在列表中(我将返回)，如果不是，添加任何A"或尚未出现在输出列表中的B"元素.

I want, given a list formed by A-B elements ([a-b,b-c,c-d]), check if some given element it's already in a list (which I will return), and if it's not, add any "A" or "B" element that is not in the output list yet.

我还没有真正找到任何足够简单"的答案让我理解(例如，我找到了一个带有映射和我从未使用或见过的东西的答案).

I haven't really found any "easy" enough answer for me to understand yet (like, I found one with mappings and stuff I've never used nor seen).

所以输出列表只需要 [a,b,c,d]

So the output list would need to only have [a,b,c,d]

我想做的是，我被这样称呼:

edit: what I'm trying to do is, I get called like this:

enumerate([a-b,b-c,c-d], EnumNodes, EnumArcs)

而且我必须返回两个列表.第一个给出节点(具有这种特定形式:

And I have to return two lists. First one gives the nodes (with this specific form:

[enum(1,a),enum(2,b),enum(3,c),enum(4,d)],

第二个给出了所述节点之间的弧(连接).

and second one gives the arcs (the conections) between said nodes.

所以我知道"如何计算和返回列表中的项目，但我不知道以下内容:

So I am at the part where I "know" how to count and return items in a list, but I do not know the following:

-如何在列表中仅插入唯一元素

-How to insert ONLY unique elements in a list

-如何首先检查A"是否在列表中，如果没有插入，然后检查B"是否在列表中，如果没有，插入它(我不知道的原因，我可以't自带调用规则的方式，一次完成，两次，每个元素一次，每一步递归，不出错

-How to first check if "A" is in the list, if not insert it, and then check if "B" is in the list, if not, insert it (reason for me not knowing this, I can't come with a way of invoking the rule, once it's done, twice, once for each element, each step of recursion, without making a mistake

推荐答案

您在寻找这样的子句吗?

Are you looking for a clause like this?

% ensure(ELEMENT, LIST_IN, LIST_OUT)

% If X is already a member of L, then the result is L
ensure(X, L, L) :-
    member(X, L), !.

% If not, the result is X appended to L
ensure(X, L, [X | L]).

使用:

1 ?- ensure(1, [1,2,3], O).
O = [1, 2, 3].

2 ?- ensure(2, [1,3], O).
O = [2, 1, 3].

<小时>

我认为这就是你正在寻找的东西......

---

I think this is the sort of thing you are looking for...

% enumerate(CONNECTIONS_IN, NODES_OUT, ARCS_OUT)

enumerate(C, N, A) :-
    enum_nodes(C, [], N, 1),
    create_arcs(C, N, A).

% enum_nodes(CONNECTIONS_IN, NODES_IN, NODES_OUT, START_ID) 
% Fills up NODES_OUT with enums. New IDs start at START_ID...

enum_nodes([], N, N, _).
enum_nodes([A-B | T], N, NOUT, ID) :-
    ensure_node(A, N, NTMP1, ID, ID1),
    ensure_node(B, NTMP1, NTMP2, ID1, ID2),
    enum_nodes(T, NTMP2, NOUT, ID2).

% ensure_node(NODE, NODES_IN, NODES_OUT, ID_IN, ID_OUT)
% Adds enum(ID_IN, NODE) to NODES_IN to produce NODES_OUT if NODE does not already exist in NODES_IN

ensure_node(NODE, NODES_IN, NODES_IN, ID, ID) :-
    member(enum(_, NODE), NODES_IN), !.

ensure_node(NODE, NODES_IN, [enum(ID_IN, NODE) | NODES_IN], ID_IN, ID_OUT) :-
    ID_OUT is ID_IN + 1.

% create_arcs(CONNECTIONS_IN, NODES_IN, ARCS_OUT).  
% Create arcs - makes a list of arc(NODE_ID_1, NODE_ID_2)...

create_arcs([], _, []).
create_arcs([A-B | T], NODES, [arc(NODE_ID_A, NODE_ID_B) | TARCS]) :-
    member(enum(NODE_ID_A, A), NODES),
    member(enum(NODE_ID_B, B), NODES),
    create_arcs(T, NODES, TARCS).

示例输出:

1 ?- enumerate([a-b, c-d, d-a], N, A).
N = [enum(4, d), enum(3, c), enum(2, b), enum(1, a)],
A = [arc(1, 2), arc(3, 4), arc(4, 1)] .

如果你做一个 trace，你可以看到它在工作......

If you do a trace, you can see it working...

2 ?- trace.
true.

[trace] 2 ?- enumerate([a-b, c-d, d-a], N, A).
   Call: (6) enumerate([a-b, c-d, d-a], _G2634, _G2635) ? creep
   Call: (7) enum_nodes([a-b, c-d, d-a], [], _G2634, 1) ? creep
   Call: (8) ensure_node(a, [], _G2740, 1, _G2742) ? creep
   Call: (9) lists:member(enum(_G2731, a), []) ? creep
   Fail: (9) lists:member(enum(_G2731, a), []) ? creep
   Redo: (8) ensure_node(a, [], _G2740, 1, _G2742) ? creep
   Call: (9) _G2747 is 1+1 ? creep
   Exit: (9) 2 is 1+1 ? creep
   Exit: (8) ensure_node(a, [], [enum(1, a)], 1, 2) ? creep
   Call: (8) ensure_node(b, [enum(1, a)], _G2749, 2, _G2751) ? creep
   Call: (9) lists:member(enum(_G2740, b), [enum(1, a)]) ? creep
   Fail: (9) lists:member(enum(_G2740, b), [enum(1, a)]) ? creep
   Redo: (8) ensure_node(b, [enum(1, a)], _G2749, 2, _G2751) ? creep
   Call: (9) _G2756 is 2+1 ? creep
   Exit: (9) 3 is 2+1 ? creep
   Exit: (8) ensure_node(b, [enum(1, a)], [enum(2, b), enum(1, a)], 2, 3) ? creep
   Call: (8) enum_nodes([c-d, d-a], [enum(2, b), enum(1, a)], _G2634, 3) ? creep
   Call: (9) ensure_node(c, [enum(2, b), enum(1, a)], _G2758, 3, _G2760) ? creep
   Call: (10) lists:member(enum(_G2749, c), [enum(2, b), enum(1, a)]) ? creep
   Fail: (10) lists:member(enum(_G2749, c), [enum(2, b), enum(1, a)]) ? creep
   Redo: (9) ensure_node(c, [enum(2, b), enum(1, a)], _G2758, 3, _G2760) ? creep
   Call: (10) _G2765 is 3+1 ? creep
   Exit: (10) 4 is 3+1 ? creep
   Exit: (9) ensure_node(c, [enum(2, b), enum(1, a)], [enum(3, c), enum(2, b), enum(1, a)], 3, 4) ? creep
   Call: (9) ensure_node(d, [enum(3, c), enum(2, b), enum(1, a)], _G2767, 4, _G2769) ? creep
   Call: (10) lists:member(enum(_G2758, d), [enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Fail: (10) lists:member(enum(_G2758, d), [enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Redo: (9) ensure_node(d, [enum(3, c), enum(2, b), enum(1, a)], _G2767, 4, _G2769) ? creep
   Call: (10) _G2774 is 4+1 ? creep
   Exit: (10) 5 is 4+1 ? creep
   Exit: (9) ensure_node(d, [enum(3, c), enum(2, b), enum(1, a)], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], 4, 5) ? creep
   Call: (9) enum_nodes([d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], _G2634, 5) ? creep
   Call: (10) ensure_node(d, [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], _G2776, 5, _G2778) ? creep
   Call: (11) lists:member(enum(_G2767, d), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (11) lists:member(enum(4, d), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (10) ensure_node(d, [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], 5, 5) ? creep
   Call: (10) ensure_node(a, [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], _G2779, 5, _G2781) ? creep
   Call: (11) lists:member(enum(_G2770, a), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (11) lists:member(enum(1, a), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (10) ensure_node(a, [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], 5, 5) ? creep
   Call: (10) enum_nodes([], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], _G2634, 5) ? creep
   Exit: (10) enum_nodes([], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], 5) ? creep
   Exit: (9) enum_nodes([d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], 5) ? creep
   Exit: (8) enum_nodes([c-d, d-a], [enum(2, b), enum(1, a)], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], 3) ? creep
   Exit: (7) enum_nodes([a-b, c-d, d-a], [], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], 1) ? creep
   Call: (7) create_arcs([a-b, c-d, d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], _G2635) ? creep
   Call: (8) lists:member(enum(_G2776, a), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (8) lists:member(enum(1, a), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Call: (8) lists:member(enum(_G2777, b), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (8) lists:member(enum(2, b), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Call: (8) create_arcs([c-d, d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], _G2774) ? creep
   Call: (9) lists:member(enum(_G2788, c), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (9) lists:member(enum(3, c), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Call: (9) lists:member(enum(_G2789, d), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (9) lists:member(enum(4, d), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Call: (9) create_arcs([d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], _G2786) ? creep
   Call: (10) lists:member(enum(_G2800, d), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (10) lists:member(enum(4, d), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Call: (10) lists:member(enum(_G2801, a), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Exit: (10) lists:member(enum(1, a), [enum(4, d), enum(3, c), enum(2, b), enum(1, a)]) ? creep
   Call: (10) create_arcs([], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], _G2798) ? creep
   Exit: (10) create_arcs([], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], []) ? creep
   Exit: (9) create_arcs([d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], [arc(4, 1)]) ? creep
   Exit: (8) create_arcs([c-d, d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], [arc(3, 4), arc(4, 1)]) ? creep
   Exit: (7) create_arcs([a-b, c-d, d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], [arc(1, 2), arc(3, 4), arc(4, 1)]) ? creep
   Exit: (6) enumerate([a-b, c-d, d-a], [enum(4, d), enum(3, c), enum(2, b), enum(1, a)], [arc(1, 2), arc(3, 4), arc(4, 1)]) ? creep
N = [enum(4, d), enum(3, c), enum(2, b), enum(1, a)],
A = [arc(1, 2), arc(3, 4), arc(4, 1)] .

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