# How to understand the contribution of edge-attributes value when multiple edges exist between two nodes? **URL:** \ **Category:** Usage\ **Tags:** R\ **Created:** [11 October 2021 11:13 UTC](https://igraph.discourse.group/t/how-to-understand-the-contribution-of-edge-attributes-value-when-multiple-edges-exist-between-two-nodes/893 "2021-10-11T11:13:40Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![peranti](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/peranti/32/594_2.png) [@peranti](https://igraph.discourse.group/u/peranti)\ **Post date:** [11 October 2021 11:13 UTC](https://igraph.discourse.group/t/how-to-understand-the-contribution-of-edge-attributes-value-when-multiple-edges-exist-between-two-nodes/893/1 "2021-10-11T11:13:40Z")
Hi, Thanks for your work and support through this package. I have a question about understanding the multiple edges and edge attributes. In my Igraph object, I have multiple edges between some of the nodes. ```auto is_simple(net_full) # [1] TRUE ``` I have identified those instances using `which_multiple(net_full)`. Now, I would like to understand how the edge.attribute values are coming from these edges individually. ```auto edge_attr(net_full, "score")[c(1898, 5892, 6556, 6746, 7443, 8267, 8564)] # [1] 161 189 310 433 917 216 324 count_multiple(net_full)[c(1898, 5892, 6556, 6746, 7443, 8267, 8564)] # [1] 2 2 2 2 2 2 2 ``` How can I find the contribution of the `161` from these `2` edges or edge types for the edge index `1898` individually? ```auto count_multiple(net_full, 1898) # [1] 2 ``` * * * This post is to continue the discussion from the Github repo, [here](https://github.com/igraph/rigraph/issues/483). ---
**Author:** ![szhorvat](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/szhorvat/32/3_2.png) [@szhorvat](https://igraph.discourse.group/u/szhorvat)\ **Post date:** [11 October 2021 12:29 UTC](https://igraph.discourse.group/t/how-to-understand-the-contribution-of-edge-attributes-value-when-multiple-edges-exist-between-two-nodes/893/2 "2021-10-11T12:29:16Z")
> [@peranti](#): > > Now, I would like to understand how the edge.attribute values are coming from these edges individually. > > ```auto > edge_attr(net_full, "score")[c(1898, 5892, 6556, 6746, 7443, 8267, 8564)] > # [1] 161 189 310 433 917 216 324 > > ``` Can you clarify the question please, perhaps with a self-contained minimal example? These values do come from individual edges. None of these values are the combination of the “score” attribute of several parallel edges. > [@peranti](#): > > How can I find the contribution of the `161` from these `2` edges or edge types for the edge index `1898` individually? Each edge has a unique index. If there are two edges between the same pair of vertices, those two edges will have different indices. 1898 refers to a single edge, not a combination of two parallel edges. ---
**Author:** ![peranti](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/peranti/32/594_2.png) [@peranti](https://igraph.discourse.group/u/peranti)\ **Post date:** [11 October 2021 12:49 UTC](https://igraph.discourse.group/t/how-to-understand-the-contribution-of-edge-attributes-value-when-multiple-edges-exist-between-two-nodes/893/3 "2021-10-11T12:49:11Z")
This may not be the efficient way of doing this. Here is what I did (but, suggestions are welcome!) * * * The first few indices from the command `c(1:11759454)[which_multiple(net_full)]` result are `c(1898, 5892, 6556, 6746, 7443, 8267, 8564)`, where the graph `net_full` contain 11759454 edges. As I mentioned above, I looked into these indices. The command `edge_attr(net_full, "score")[1898]` resulted in `161`. When I looked into `count_multiple(net_full)[1898]`, it resulted in `2`. I want to know how to find these `2`. When I looked into the `get.edge.ids(net_full, c("N233", "N412"))`, it resulted only one edge id. Is it something as expected? If I understand clearly, your reply, there should be 2 edge ids, right? ---
**Author:** ![szhorvat](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/szhorvat/32/3_2.png) [@szhorvat](https://igraph.discourse.group/u/szhorvat)\ **Post date:** [11 October 2021 12:54 UTC](https://igraph.discourse.group/t/how-to-understand-the-contribution-of-edge-attributes-value-when-multiple-edges-exist-between-two-nodes/893/4 "2021-10-11T12:54:22Z")
Please see the discussion here: > > > I would expect the following to return \`1, 2, 3\` instead of \`3\`: > > \`\`\` > \> g \<- …make\_graph(c(1,2, 1,2, 1,2)) > \> get.edge.ids(g, c(1,2), multi=T) > \[1\] 3 > \`\`\` > > I am using the current \`dev\` branch. > > The relevant function should be: > > https://github.com/igraph/rigraph/blob/dev/tools/stimulus/rinterface.c.in#L8363 > > which dispatches to \`igraph\_get\_eids\_multi()\` as it should. What am I misunderstanding here, and why does it not work? > > Not being familiar enough with R/igraph internals yet, it is unclear to me what \`C\_R\_igraph\_get\_eids\` is. Does it map to \`igraph\_get\_eids\` through stimulus (which would explain the behaviour) or to \`R\_igraph\_get\_eids\` (which is what should happen)? `get.edge.ids` returns as many edge IDs as the size of the input. To get the IDs of both edges between these two vertices, you can use ``` get.edge.ids(net_full, c("N233", "N412", "N233", "N412")) ``` Another important point is that `which_multiple` does not return `TRUE` for the first edge between any pair of vertices, only for the 2nd, 3rd, etc. ---
**Author:** ![szhorvat](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/szhorvat/32/3_2.png) [@szhorvat](https://igraph.discourse.group/u/szhorvat)\ **Post date:** [11 October 2021 12:57 UTC](https://igraph.discourse.group/t/how-to-understand-the-contribution-of-edge-attributes-value-when-multiple-edges-exist-between-two-nodes/893/5 "2021-10-11T12:57:39Z")
Can you explain in more detail why you want to get all edge IDs for groups of parallel edges? I can imagine several possibilities, but I would like to know _your_ actual motivation. Having some real-world use cases helps us decide on the best interface. ---
**Author:** ![peranti](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/peranti/32/594_2.png) [@peranti](https://igraph.discourse.group/u/peranti)\ **Post date:** [8 November 2021 10:56 UTC](https://igraph.discourse.group/t/how-to-understand-the-contribution-of-edge-attributes-value-when-multiple-edges-exist-between-two-nodes/893/6 "2021-11-08T10:56:11Z")
@szhorvat It is merely for understanding purposes; how edge.attribute values are grouped from each of the edges between a pair of nodes. * * * _Edit:_ I will get back to you on this with more details. ---
**Author:** ![szhorvat](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/szhorvat/32/3_2.png) [@szhorvat](https://igraph.discourse.group/u/szhorvat)\ **Post date:** [8 November 2021 11:07 UTC](https://igraph.discourse.group/t/how-to-understand-the-contribution-of-edge-attributes-value-when-multiple-edges-exist-between-two-nodes/893/7 "2021-11-08T11:07:16Z")
Yes, of course that makes sense, and we are discussing how to make improvements for future versions. I asked because the perspective of users is very valuable when making decisions about such issues.