如何以编程方式访问 Mathematica 8 中“Graph”对象的信息？

发布于 2024-11-15 11:41:38 字数 1252 浏览 2 评论 0原文

我正在尝试访问 Mathematica 8 中 Graph 对象内的信息。由于某种原因，Part 命令似乎不起作用。

myGraph 是我想要访问的对象。

下面的第一行显示 myGraph。其他人的作用是检查它。

myGraph

myGraph // FullForm  
myGraph // InputForm  
myGraph // OutputForm    
myGraph[[1]]
myGraph[[2]]

myGraph

为什么 myGraph[[1]] 不返回 List[1, 3,4,2,5]？ [我检查到级别 2，以防 Graph 被某些不可见的包装器包装。 Level[myGraph,1]，仅返回 {}。 FullForm[myGraph][[1]] 返回图表本身的图片。

我一定是忽略了一些显而易见的事情。

编辑

这是我用来生成图表的代码。其中大部分与当前的问题无关。但至少您将使用我正在使用的相同代码。

ClearAll[edges, compatibleQ, adjacentCourses, g];
edges[w_, b_] := 
 Most /@ Accumulate /@ 
   Flatten[Permutations[#] & /@ IntegerPartitions[w, All, b], 1]

compatibleQ[j_, k_, edg_] := 
 If[Intersection[edg[[j]], edg[[k]]] == {}, {j, k}, False]

adjacentCourses[edg_] := 
 Module[{len = Length[edg]},
  Cases[Flatten[Table[compatibleQ[j, k, edg], {j, len}, {k, j, len}], 
    1], {v_, w_} :>  v \[UndirectedEdge] w]]

myGraph =  Graph[adjacentCourses[edges[9, {2, 3}]], VertexLabels -> "Name", 
ImagePadding -> 10]

原文

I'm trying to access information within a Graph object in Mathematica 8. For some reason, the Part command does not seem to work.

myGraph is the object I want to gain access to.

The first line below displays myGraph. The others serve to inspect it.

myGraph

myGraph // FullForm  
myGraph // InputForm  
myGraph // OutputForm    
myGraph[[1]]
myGraph[[2]]

myGraph

Why doesn't myGraph[[1]] return List[1,3,4,2,5] ?
[I checked to level 2 just in case Graph were wrapped by some invisible wrapper. Level[myGraph,1], simply returns {}. And FullForm[myGraph][[1]] returns a picture of the graph itself.

I must be overlooking something obvious.

Edit

Here's the code I used to produce the graph. Most of it is irrelevant to the issue at hand.
But at least you'll be working with the same code I am using.

ClearAll[edges, compatibleQ, adjacentCourses, g];
edges[w_, b_] := 
 Most /@ Accumulate /@ 
   Flatten[Permutations[#] & /@ IntegerPartitions[w, All, b], 1]

compatibleQ[j_, k_, edg_] := 
 If[Intersection[edg[[j]], edg[[k]]] == {}, {j, k}, False]

adjacentCourses[edg_] := 
 Module[{len = Length[edg]},
  Cases[Flatten[Table[compatibleQ[j, k, edg], {j, len}, {k, j, len}], 
    1], {v_, w_} :>  v \[UndirectedEdge] w]]

myGraph =  Graph[adjacentCourses[edges[9, {2, 3}]], VertexLabels -> "Name", 
ImagePadding -> 10]

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夏夜暖风 2024-11-22 11:41:38

不管外表如何，Mathematica 8 中引入的图形对象并不是“正常”的符号表达式。以下SO问题详细讨论了这个问题和其他此类问题，包括提取部分图形定义的方法：

Mathematica 8.0中的新图形

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奶气 2024-11-22 11:41:38

事实证明，我的问题有一些简单的答案。

Graph 的文档包含多种从 Graph 对象检索信息的方法。（对我没有检查感到羞耻。）在我看来，最有用的命令是：

VertexList[]
VertexCount[]
EdgeList[]
EdgeCount[]
EdgeRules[] 
VertexIndex[]
EdgeIndex[]
PropertyValue[]

通常在操作图形对象之后，我们需要从图形对象中获取信息。
我可以轻松找到我构建的图表中包含哪些信息，但如果输出派生图表（例如从 NeighborhoodGraph 中），则无需探测我就无法知道其属性。

感谢 @dbJohn 提供 Wolfram 文档的链接。

特别感谢 @WReach 在之前的 SO 讨论中提供了他的评论的链接关于Graph对象。

Turns out that there were some straightforward answers to my question.

The documentation for Graph contains several ways of retrieving information from a Graph object. (Shame on me for not checking.) The most useful commands, in my view, are:

VertexList[]
VertexCount[]
EdgeList[]
EdgeCount[]
EdgeRules[] 
VertexIndex[]
EdgeIndex[]
PropertyValue[]

We need to get information OUT of the graph object typically after we've manipulated it.
I can easily find what information went into a Graph I build but if a derivative Graph is output, e.g. from NeighborhoodGraph, I won't know its properties without probing.

Thanks to @dbJohn for the link to the Wolfram documentation.

Special thanks to @WReach for the link to his comments in a prior SO discussion about the Graph object.

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