I tried using the union function on 2 graphs which where inducted subgraph of the same graph G (so there was no conflict among them).

My problem is the original graph (and the subgraphs) are weighted, on the other hand the union of those subgraphs is not.

This is the code i created the subgraphs with (weights can assume a value in {1, 2, 3, 4, 5}:

```
weights <- E(g)$weight
graphs <- list()
for (r in seq(5)) {
graphs[[r]] <- delete.edges(g, E(g)[weights!=r])
}
reduced_graphs <- list()
x <- numeric(5)
y <- numeric(5)
for (r in seq(5)) {
reduced_graphs[[r]] <- delete.vertices(graphs[[r]], V(graphs[[r]])[degree(graphs[[r]])<=-1])
y[r] <- length(get_users(reduced_graphs[[r]]))
reduced_graphs[[r]] <- induced_subgraph(reduced_graphs[[r]], c(sample(get_users(reduced_graphs[[r]]), y[r]^sqrt(4.3/10)), get_movies(reduced_graphs[[r]])))
x[r] <- length(get_movies(reduced_graphs[[r]]))
reduced_graphs[[r]] <- induced_subgraph(reduced_graphs[[r]], c(sample(get_movies(reduced_graphs[[r]]), x[r]^(4.3/10)), get_users(reduced_graphs[[r]])))
reduced_graphs[[r]] <- delete.vertices(reduced_graphs[[r]], V(reduced_graphs[[r]])[degree(reduced_graphs[[r]])==0])
}
```

And this is the code that gives me an issue:

```
reduced_graph <- igraph::union(reduced_graphs[[1]], reduced_graphs[[2]])
is_weighted(reduced_graph)
[1] FALSE
is_weighted(reduced_graphs[[1]])
[1] TRUE
is_weighted(reduced_graphs[[2]])
[1] TRUE
```

It also turn out that the vertex of the resulting graphs lost their other attributes as well (like type and color):

```
V(reduced_graph)$type
NULL
V(reduced_graph)$color
NULL
```

Does anyone know how to fix the issue? Thankyou!

OS: Windows 10 pro

Rstudio

igraph version: 1.2.6