Add Graph Node Names, Edge Weights, and Other Attributes

This example shows how to add attributes to the nodes and edges in graphs created using graph and digraph. You can specify node names or edge weights when you originally call graph or digraph to create a graph. However, this example shows how to add attributes to a graph after it has been created.

Create Graph

Create a directed graph. The corresponding elements in s and t define the source and target nodes of each edge in the graph.

s = [1 1 2 2 3];
t = [2 4 3 4 4];
G = digraph(s,t)

G = 
  digraph with properties:

    Edges: [5x1 table]
    Nodes: [4x0 table]

Add Node Names

Add node names to the graph by adding the variable, Name, to the G.Nodes table. The Name variable must be specified as an N-by-1 cell array of character vectors or string array, where N = numnodes(G). It is important to use the Name variable when adding node names, as this variable name is treated specially by some graph functions.

G.Nodes.Name = {'First' 'Second' 'Third' 'Fourth'}';

View the new Nodes table.

G.Nodes

ans=4×1 table
       Name   
    __________

    {'First' }
    {'Second'}
    {'Third' }
    {'Fourth'}

Use table indexing to view the names of nodes 1 and 4.

G.Nodes.Name([1 4])

ans = 2x1 cell
    {'First' }
    {'Fourth'}

Add Edge Weights

Add edge weights to the graph by adding the variable, Weight, to the G.Edges table. The Weight variable must be an M-by-1 numeric vector, where M = numedges(G). It is important to use the Weight variable when adding edge weights, as this variable name is treated specially by some graph functions.

G.Edges.Weight = [10 20 30 40 50]';

View the new Edges table.

G.Edges

ans=5×2 table
            EndNodes            Weight
    ________________________    ______

    {'First' }    {'Second'}      10  
    {'First' }    {'Fourth'}      20  
    {'Second'}    {'Third' }      30  
    {'Second'}    {'Fourth'}      40  
    {'Third' }    {'Fourth'}      50  

Use table indexing to view the first and third rows of G.Edges.

G.Edges([1 3],:)

ans=2×2 table
            EndNodes            Weight
    ________________________    ______

    {'First' }    {'Second'}      10  
    {'Second'}    {'Third' }      30  

Add Custom Attributes

In principle you can add any variable to G.Nodes and G.Edges that defines an attribute of the graph nodes or edges. Adding custom attributes can be useful, since functions like subgraph and reordernodes preserve the graph attributes.

For example, add a variable named Power to G.Edges to indicate whether each edge is 'on' or 'off'.

G.Edges.Power = {'on' 'on' 'on' 'off' 'off'}';
G.Edges

ans=5×3 table
            EndNodes            Weight     Power 
    ________________________    ______    _______

    {'First' }    {'Second'}      10      {'on' }
    {'First' }    {'Fourth'}      20      {'on' }
    {'Second'}    {'Third' }      30      {'on' }
    {'Second'}    {'Fourth'}      40      {'off'}
    {'Third' }    {'Fourth'}      50      {'off'}

Add a variable named Size to G.Nodes to indicate the physical size of each node.

G.Nodes.Size = [10 20 10 30]';
G.Nodes

ans=4×2 table
       Name       Size
    __________    ____

    {'First' }     10 
    {'Second'}     20 
    {'Third' }     10 
    {'Fourth'}     30 

Modify Tables with Variables Editor

Since Nodes and Edges are both tables, you can use the Variables editor to interactively view or edit the tables. For more information, see Create and Edit Variables.

Label Nodes and Edges of Graph Plot

When you plot a graph, you can use the variables in G.Nodes and G.Edges to label the graph nodes and edges. This practice is convenient, since these variables are already guaranteed to have the correct number of elements.

Plot the graph and label the edges using the Power variable in G.Edges. Label the nodes using the Size variable in G.Nodes.

p = plot(G,'EdgeLabel',G.Edges.Power,'NodeLabel',G.Nodes.Size)

p = 
  GraphPlot with properties:

     NodeColor: [0 0.4470 0.7410]
    MarkerSize: 4
        Marker: 'o'
     EdgeColor: [0 0.4470 0.7410]
     LineWidth: 0.5000
     LineStyle: '-'
     NodeLabel: {'10'  '20'  '10'  '30'}
     EdgeLabel: {'on'  'on'  'on'  'off'  'off'}
         XData: [2 1.5000 1 2]
         YData: [4 3 2 1]
         ZData: [0 0 0 0]

  Use GET to show all properties