[igraph] Potential igraph issue: Initial assignment of zeroth vertex attribute

[Magnus]

Assigning a value to the zeroth vertex attribute for the first time 
seems to
result in every single vertex receiving the value in question. Assigning
attributes for other vertices, or reassigning the zeroth vertex, seems to
work as expected.

Best,
Magnus

ps. Thanks so much for igraph. Regardless of these two issues,
(which might end up getting explained), it is great software, and a
boon to network researchers in all fields.

> g <- graph.ring(10)
> V(g)[1]$a
NULL
>
> V(g)[1]$a <- "Value"
> V(g)[0]$a
[1] NA
> V(g)[1]$a
[1] "Value"
> V(g)[2]$a
[1] NA
>
> stopifnot( is.null(V(g)[2]$a) | is.na(V(g)[2]$a) )
> print("OK so far")
[1] "OK so far"
>
> g <- graph.ring(10)
> V(g)[0]$a
NULL
>
> V(g)[0]$a <- "Value"
> V(g)[0]$a
[1] "Value"
> V(g)[1]$a
[1] "Value"
> V(g)[2]$a
[1] "Value"
>
> stopifnot( is.null(V(g)[2]$a) | is.na(V(g)[2]$a) )
Error: is.null(V(g)[2]$a) | is.na(V(g)[2]$a) is not TRUE
> print("Gosh, this failed")
[1] "Gosh, this failed"
>
>
> V(g)[0]$a <- "NewValue"
> V(g)[0]$a
[1] "NewValue"
> V(g)[1]$a
[1] "Value"
> V(g)[2]$a
[1] "Value"
> print("Changing the zeroth value after first assignment works as
> expected")
[1] "Changing the zeroth value after first assignment works as expected"