Dear all,

I am using the package igraph and try to use the neighbors() function. I am

a bit confused, see the following :

Given a graph g with 18 vertices. Names of the vertices are indicated by :

> V(irt.graph)$name

[1] "AT2G41240" "AT3G13610" "AT3G02470" "AT3G30775" "AT3G18290"

"AT4G13770" "AT1G01580" "AT4G19690" "AT1G56430" "AT3G56970"

[11] "AT3G02468" "AT2G43590" "AT4G32410" "AT5G25610" "AT5G13750"

"AT5G13740" "AT4G38770" "AT5G02780"

I want to know the neighbors of my vertices.

I have :

> neighbors(g,0)

[1] 4 7 9 17

AND also :

> V(g)$name[0]

character(0)

That 1st confused me, but I thought that indices count from 1 with the V()

function but from 0 in the neighbors() funtion.

But :

For example, to know the neighbors of my first vertex "AT2G41240"

> V(g)$name[1]

[1] "AT2G41240"

> neighbors(g,V(g)$name=="AT2G41240")

[1] 7 9

or I had (just above) :

> neighbors(g,0)

[1] 4 7 9 17

I know that AT2G41240 has 4 neighbors,

thus

> neighbors(g,V(g)$name=="AT2G41240")

[1] 7 9

does not give to me neighbors of AT2G41240 but of another vertex,

and also :

I know the indices of the 4 neighbors of my vertex

are NOT

> V(g)$name[c(4,7,9,17)]

but in reality :

> V(g)$name[c(5,8,10,18)]

My problem is that I really would like to run the neighbors() function with

the name of my vertex and not to have to add or substract 1 to the indice

of my vertex ....

Thanks a lot,

Florence.

> sessionInfo()

R version 2.10.1 (2009-12-14)

i386-apple-darwin8.11.1

other attached packages:

[1] igraph_0.5.4-1

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