How to find out isolated subgraph?

A large graph can has multiple isolated subgraph(which is not connected with the main graph). How can I count total number of isolated subgraph? And how can I find out total number of nodes and edges in each isolated subgraph? I have a directed signed graph.

This is the code I am using:

s = [1 1 1 2 2 2 8 8 8 8];
t = [2 3 4 5 6 7 9 10 11 12];
weight= [1 -1 1 -1 1 -1 -1 1 -1 1];
G = digraph(s,t,weight);
plot(G,'Layout','force','EdgeLabel',G.Edges.Weight)
weak_bins1 = conncomp(G,'Type','weak')
component= max(weak_bins1)

Answer 1

[Christine Tobler]

The component output in your code is the number of components.

You can use the second output of conncomp to get a vector containing the number of nodes in each of the components.

To get the number of edges, you can either use the subgraph command for a specific component and then call numedges on the resulting graph. Or you can use the groupsummary function to sum up the out-degree of all nodes that are part of each component.

>> [weak_bins1, compNumNodes] = conncomp(G,'Type','weak')
weak_bins1 =
     1     1     1     1     1     1     1     2     2     2     2     2

compNumNodes =
     7     5

>> numedges(subgraph(G, find(weak_bins1 == 1)))
ans =
     6
>> numedges(subgraph(G, find(weak_bins1 == 2)))
ans =
     4
     
>> compNumEdges = groupsummary(outdegree(G), weak_bins1', 'sum')
compNumEdges =
     6
     4

[Mouli Sarkar]

numedges(subgraph(G, find(weak_bins1 == 1)))

Can this logic be more genelarized?

[Walter Roberson]

uwb = reshape(unique(weak_bins1), 1, []);
for wbn = uwb
   numedges(subgraph(G, find(weak_bins1 == wbn)))
end

but the groupsummary() that Christine shows is calculating the values for you. About the only thing to add might be

[compNumEdges, wbg] = groupsummary(outdegree(G), weak_bins1', 'sum')
[wbg, compNumEdges]

to give an array showing the weak_bin number before the count.