python 圖形

圖表是一組對象通過鏈接連接的一組對象的圖形表示。互連對象由稱為頂點的點表示，連接頂點的鏈接稱為邊。我們的教程在這里詳細(xì)描述了與圖形相關(guān)的各種術(shù)語和功能。在本章中，我們將看到如何使用python程序創(chuàng)建圖形并向其添加各種數(shù)據(jù)元素。以下是我們在圖表上執(zhí)行的基本操作。

• 顯示圖形頂點
• 顯示圖形邊緣
• 添加一個頂點
• 添加邊緣
• 創(chuàng)建一個圖

可以使用python字典數(shù)據(jù)類型輕松呈現(xiàn)圖形。我們將頂點表示為字典的關(guān)鍵字，頂點之間的連接也稱為邊界，作為字典中的值。

看看下面的圖表 -

在上面的圖中

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

我們可以在下面的python程序中展示這個圖。

# 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)

當(dāng)上面的代碼被執(zhí)行時，它會產(chǎn)生以下結(jié)果 -

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

顯示圖形頂點

為了顯示圖形頂點，我們簡單地找到圖形字典的關(guān)鍵字。我們使用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())

當(dāng)上面的代碼被執(zhí)行時，它會產(chǎn)生以下結(jié)果 -

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

顯示圖形邊緣

尋找圖形邊緣比頂點少一些，因為我們必須找到每對頂點之間的邊緣。因此，我們創(chuàng)建一個空邊列表，然后迭代與每個頂點關(guān)聯(lián)的邊值。一個列表形成了包含從頂點找到的不同組的邊。

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())

當(dāng)上面的代碼被執(zhí)行時，它會產(chǎn)生以下結(jié)果 -

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

添加一個頂點

添加一個頂點是直接向我們添加另一個關(guān)鍵字到圖形字典。

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())

當(dāng)上面的代碼被執(zhí)行時，它會產(chǎn)生以下結(jié)果 -

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

添加邊緣

將邊添加到現(xiàn)有圖涉及將新頂點視為元組并驗證邊是否已經(jīng)存在。如果不是，則添加邊緣。

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())

當(dāng)上面的代碼被執(zhí)行時，它會產(chǎn)生以下結(jié)果 -

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