保持Graphviz中节点的水平顺序

我有以下点文件内容：

digraph G {
    start -> {a0, b0} -> end;
    start -> c0 -> c1 -> c2 -> end;
    start -> d0 -> d1 -> d2 -> end;
    start -> {e0, f0} -> end;

    subgraph cluster_test {
        {
            rank = same;
            a0; b0; c0; d0; e0; f0;
        }

        {
            rank = same;
            c1; d1;
        }

        {
            rank = same;
            c2; d2;
        }
    }
}

结果图如下所示：

我想要的是保持0级节点的顺序，也就是说，我想要a0，b0在水平方向上位于c0，d0之前

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如何实现这一点？

空节点、带权重的边以及集群中最上面一行的显式排序都有帮助。请参见下面带有注释的代码：

digraph so 
{
    // we define all nodes in the beginning, before edges and clusters
    // may not be essential but I think it's good practice
    start
    a0 b0 c0 d0 e0 f0
    c1 d1 
    c2 d2
    end
    // we define "empty" nodes that can be used to route the edges
    node[ shape = point, height = 0 ];
    ax bx ex fx

    subgraph cluster_test 
    {
        // we need to keep explicit order of the top nodes in the cluster
        { rank = same; a0 -> b0 -> c0 -> d0 -> e0 ->  f0[ style = invis ] }
        // the original layout in the cluster, empty nodes added at the bottom
        { rank = same; c1 d1 }
        { rank = same; ax bx c2 d2 ex fx }
        c0 -> c1 -> c2;
        d0 -> d1 -> d2;
        // routing through invisible nodes keeps the position of all other nodes
        // edges with no arrowheads, strong weight to keep it vertical
        edge[ dir = none, weight = 10 ]
        a0 -> ax;
        b0 -> bx;
        e0 -> ex;
        f0 -> fx;
    }

    // connecting to the start and end node, normal edges again
    edge[ weight = 1, dir = forw ];
    start -> { a0 b0 c0 d0 e0 f0 }
    { ax bx  c2 d2 ex fx } -> end;
}

这给了你

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虽然在技术上是正确的，但对于一般用例来说，这种实现有点过头了。大多数StackOverflowers可能需要，而不是。tl；dr：只需在（可能的）不可见列中有问题的水平节点之间使用不可见的定向边来强制排序。你是对的@Cecil Curry-我回答了OP没有问的一个问题（如何在子图中保持边垂直）。你提到的解决方案是我答案的一部分，但被不必要的噪音弄糊涂了。