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## [igraph] Calculating average shortest path

**From**: |
Claudia Muller-Birn |

**Subject**: |
[igraph] Calculating average shortest path |

**Date**: |
Sat, 5 Mar 2011 23:53:14 +0100 |

Dear all,
I have a rather simple question regarding calculating the average shortest path
length. There are actually to ways calculating it and I am wondering why I get
two different results. Here is my toy example:
>* g1 <- graph( c( 0,1, 1,2, 2,1, 2,3 ), directed=FALSE )*
>* g2 <- graph( c( 0,1, 1,2, 2,1, 2,3 ), directed=TRUE )*
First possibility to calculate the average shortest path (or is it just one
path???)
>* average.path.length(g1, directed=FALSE)*
[1] 1.666667
>* average.path.length(g2, directed=TRUE)*
[1] 1.571429
Second possibility would be by just calling the mean
>* sp1 <- shortest.paths(g1)*
>* mean(sp1,na.rm=TRUE)*
[1] 1.25
>* sp2 <- shortest.paths(g2, v=V(g2), mode='out')*
>* sp2[is.infinite(sp2)]<-NA*
>* mean(sp2,na.rm=TRUE)*
[1] 1
In my opinion, the second way to calculate the average shortest paths makes
much more sense but then I am wondering about the meaning and calculation of
the first possibility based on average.path.length. How is the latter function
implemented or do I miss some settings?
Thank you very much for any help or idea.
Best,
Claudia

**[igraph] Calculating average shortest path**,
*Claudia Muller-Birn* **<=**