Python - 图表

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图表是一组对象的图形表示，其中一些对象对通过链接连接。互连的对象由称为顶点的点表示，连接顶点的链接称为边。我们的教程中详细描述了与图表相关的各种术语和功能。

在本章中，我们将了解如何使用 python 程序创建图形并向其中添加各种数据元素。以下是我们在图表上执行的基本操作。

• 显示图形顶点
• 显示图形边缘
• 添加顶点
• 添加边缘
• 创建图表

使用 python 字典数据类型可以轻松呈现图形。我们将顶点表示为字典的键，将顶点之间的连接（也称为边）表示为字典中的值。

看一下下图 -

在上图中，

V = {a, b, c, d, e}
E = {ab, ac, bd, cd, de}

例子

我们可以在 python 程序中呈现该图，如下所示 -

# Create the dictionary with graph elements
graph = { 
   "a" : ["b","c"],
   "b" : ["a", "d"],
   "c" : ["a", "d"],
   "d" : ["e"],
   "e" : ["d"]
}
# Print the graph 		 
print(graph)

输出

执行上述代码时，会产生以下结果 -

{'c': ['a', 'd'], 'a': ['b', 'c'], 'e': ['d'], 'd': ['e'], 'b': ['a', 'd']}

显示图形顶点

为了显示图形顶点，我们简单地找到图形字典的键。我们使用keys()方法。

class graph:
   def __init__(self,gdict=None):
      if gdict is None:
         gdict = []
      self.gdict = gdict
# Get the keys of the dictionary
   def getVertices(self):
      return list(self.gdict.keys())
# Create the dictionary with graph elements
graph_elements = { 
   "a" : ["b","c"],
   "b" : ["a", "d"],
   "c" : ["a", "d"],
   "d" : ["e"],
   "e" : ["d"]
}
g = graph(graph_elements)
print(g.getVertices())

输出

执行上述代码时，会产生以下结果 -

['d', 'b', 'e', 'c', 'a']

显示图形边缘

查找图的边比查找顶点稍微复杂一些，因为我们必须找到中间有一条边的每一对顶点。因此，我们创建一个空的边列表，然后迭代与每个顶点关联的边值。形成一个列表，其中包含从顶点找到的不同边组。

class graph:
   def __init__(self,gdict=None):
      if gdict is None:
         gdict = {}
      self.gdict = gdict

   def edges(self):
      return self.findedges()
# Find the distinct list of edges
   def findedges(self):
      edgename = []
      for vrtx in self.gdict:
         for nxtvrtx in self.gdict[vrtx]:
            if {nxtvrtx, vrtx} not in edgename:
               edgename.append({vrtx, nxtvrtx})
      return edgename
# Create the dictionary with graph elements
graph_elements = { 
   "a" : ["b","c"],
   "b" : ["a", "d"],
   "c" : ["a", "d"],
   "d" : ["e"],
   "e" : ["d"]
}
g = graph(graph_elements)
print(g.edges())

输出

执行上述代码时，会产生以下结果 -

[{'b', 'a'}, {'b', 'd'}, {'e', 'd'}, {'a', 'c'}, {'c', 'd'}]

添加顶点

添加顶点很简单，我们向图字典中添加另一个附加键。

例子

class graph:
   def __init__(self,gdict=None):
      if gdict is None:
         gdict = {}
      self.gdict = gdict
   def getVertices(self):
      return list(self.gdict.keys())
# Add the vertex as a key
   def addVertex(self, vrtx):
      if vrtx not in self.gdict:
         self.gdict[vrtx] = []
# Create the dictionary with graph elements
graph_elements = { 
   "a" : ["b","c"],
   "b" : ["a", "d"],
   "c" : ["a", "d"],
   "d" : ["e"],
   "e" : ["d"]
}
g = graph(graph_elements)
g.addVertex("f")
print(g.getVertices())

输出

执行上述代码时，会产生以下结果 -

['a', 'b', 'c', 'd', 'e','f']

添加边缘

向现有图添加边涉及将新顶点视为元组并验证边是否已存在。如果不是，则添加边缘。

class graph:
   def __init__(self,gdict=None):
      if gdict is None:
         gdict = {}
      self.gdict = gdict
   def edges(self):
      return self.findedges()
# Add the new edge
   def AddEdge(self, edge):
      edge = set(edge)
      (vrtx1, vrtx2) = tuple(edge)
      if vrtx1 in self.gdict:
         self.gdict[vrtx1].append(vrtx2)
      else:
         self.gdict[vrtx1] = [vrtx2]
# List the edge names
   def findedges(self):
      edgename = []
      for vrtx in self.gdict:
         for nxtvrtx in self.gdict[vrtx]:
            if {nxtvrtx, vrtx} not in edgename:
               edgename.append({vrtx, nxtvrtx})
        return edgename
# Create the dictionary with graph elements
graph_elements = { 
   "a" : ["b","c"],
   "b" : ["a", "d"],
   "c" : ["a", "d"],
   "d" : ["e"],
   "e" : ["d"]
}
g = graph(graph_elements)
g.AddEdge({'a','e'})
g.AddEdge({'a','c'})
print(g.edges())

输出

执行上述代码时，会产生以下结果 -

[{'e', 'd'}, {'b', 'a'}, {'b', 'd'}, {'a', 'c'}, {'a', 'e'}, {'c', 'd'}]