Wrong network construction for networks with no edges and more than one node

[bockthom]

Description

When we construct a network which has zero edges and more than one node, all the nodes get combined to one single node.

Thanks to @SCPhantom for pointing this out!

Steps to Reproduce or Minimal Working Example (MWE)

The MWE of @SCPhantom:

1. Replace the content of the file ./sample/results/testing/sample_feature/feature/commits.list by the following lines:

1;"2016-07-12 15:58:59";"D1";"[email protected]";"2016-07-12 15:58:59";"D1";"[email protected]";"6409a8f399b81919729d14554b923d494b6b4229";1;1;1;2;"a1.c";"A1";"Feature";1

2;"2016-07-12 15:59:10";"D2";"[email protected]";"2016-07-12 15:59:10";"D2";"[email protected]";"722ca215917e3f22348b993acfc4fae578b4a4c9";1;1;1;2;"a1.c";"A2";"Feature";1

2. Run the following lines in R:

source("codeface-extraction-r/util-init.R", chdir = TRUE)

DATA.PATH ="codeface-extraction-r/sample"
CASESTUDY = "sample"
ANALYSIS.RANGE.TYPE <- "testing"

ARTIFACT = "feature"
AUTHOR.RELATION = "cochange"
ARTIFACT.RELATION <- "cochange"

proj.conf = ProjectConf$new(DATA.PATH, ANALYSIS.RANGE.TYPE, CASESTUDY, ARTIFACT)
proj.data = ProjectData$new(proj.conf)


net.conf = NetworkConf$new()

net.conf$update.values(list(author.relation = AUTHOR.RELATION,
                            artifact.relation = ARTIFACT.RELATION,
                            base.artifact.edges = F,
                            simplify = F))

net.builder = NetworkBuilder$new(proj.data, net.conf)

network = net.builder$get.author.network()

pdf(file = "network_sample_feature_filter_base.pdf", width = 8, height = 5)
plot.network(network)
dev.off()

The resulting network should contain two nodes, namely "D1" and "D2". However, currently there is only one node:

Versions

This affects several versions. I tested it with v3.4.

Problem & Solution

After debugging the above stated MWE, I identified a bug in line 1041 of util-networks.R:

https://github.com/se-passau/codeface-extraction-r/blob/83513c701a1cd013aff5ebda152e2b38789d04e3/util-networks.R#L1039-L1042

Here, nodes.processed is a data.frame containing the developers "D1" and "D2" as rows (one column). Hence, igraph::vertices(nodes.processed) treats this column vector as one node (for whatever reason, I did not find anything about that in the documentation of igraph).

Solution: Transpose the data.frame! (Use t function). The end of line 1041 should look like the following:

igraph::vertices(t(nodes.processed))

This solves the problem! We now have two columns and therefore two nodes "D1" and "D2"!

I will provide a patch for that very soon!

[clhunsen]

Thank you both for working on this! This is a regression introduced during the addition of the muti-relation networks (somewhere between v3.1 and v3.2).

Instead of simply transposing the data.frame, we should go to use igraph::graph.data.frame and create.empty.edge.list instead. I am currently working on an additional patch to introduce this change and a corresponding test to prevent the issue in the future.

[clhunsen]

Here the gist with my proposed patch: https://gist.github.com/clhunsen/f6332ceac29630476ecbe816839846d8.

[clhunsen]

With the merging of PR #149, this can be closed.