Re: [igraph] Error in using the function subcomponent( )

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Thank you.

 

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address@hidden

 

From: Gábor Csárdi

Date: 2014-02-24 22:45

To: Help for igraph users

Subject: Re: [igraph] Error in using the function subcomponent( )

On Mon, Feb 24, 2014 at 9:29 AM, address@hidden <address@hidden> wrote:

Hi!

 

Thanks for your kind reply. But I still have two question about the function subcomponent( ):

 

1. Should not the result of " subcomponent(g, 4, "all")" be the union of "subcomponent(g, 4, "in")" and "subcomponent(g, 4, "out")"?

No. Just calculate it by hand for your graph.

 

2. The graph is a directed network with 10 vertices and 10 edges and the vertice 0 is an isolated node.

Yes, because vertices are numbered from zero in an 'edgelist' file.

Even if  4 in the source code is 5 in the graph, the result of subcomponent(g, 4, "out") is supposed to be NULL, because there is no vertice could be reached from vertice 5 in graph.

You need to add one to the numbers in the file, to get the ids in R igraph. So when you write subcomponent(g, 4, "out") that belongs to vertex 3 in your file. Which does have an outgoing edge, so subcomponent(g, 4, "out") will be c(4, 3) I guess

The result will never be NULL, anyway, as it always contains the vertex itself.

G.

 

 

Here is the graph: 

1   5

1   7

3   2

4   5

4   7

4   9

9   4

6   9

8   7

9   2

 

best

Xueming

 

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address@hidden

 

From: Gábor Csárdi

Date: 2014-02-23 23:42

To: Help for igraph users

Subject: Re: [igraph] Error in using the function subcomponent( )

Hi!

On Sun, Feb 23, 2014 at 9:43 AM, address@hidden <address@hidden> wrote:

Hello!

 

I am trying to use the subcomponent() to find the in-component and out-component from a given vertice.

Here is the source code and result:

 

> g<-read.graph("input.txt", "edgelist")

The "edgelist" file format is indexed from zero, so what is 4 in your file will be 5 in your graph.

Gabor

 

> subcomponent(g, 4, "in")

[1] 4

> subcomponent(g, 4, "out")

[1] 4 3

> subcomponent(g, 4, "all")

[1]  4  3 10  5  7  6  8  2  9

 

Here is the input file "input.txt" (a directed network with 10 nodes and 10 edges):

1   5

1   7

3   2

4   5

4   7

4   9

9   4

6   9

8   7

9   2

 

But the actual result is should be:

subcomponent(g, 4, "in"):  4 6 9

subcomponent(g, 4, "out"):  2 4 5 7 9

subcomponent(g, 4, "all"):  2 4 5 6 7 9

 

Why is the results computed by using the function subcomponent( ) different from the actual result?

 

best

Xueming

 

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