# Getting started with rgexf

#### George G. Vega Yon

#### August 11, 2021

# Introduction

The `rgexf` package provides a way to interact with GEXF files. The GEXF standard was developed by the Gephi–“Like Photoshop for graphs”–core team, and can be used to save static and dynamic networks.

With the `rgexf` package, users can create `gexf` (R) objects from scratch, import GEXF files, coerce `gexf` objects into `igraph` objects, and visualize graphs using the `gexf-js` JavaScript library. In this vignette, we will illustrate how can we (a) import a GEXF file into R and visualize it with `igraph,` and (b) create a `gexf` object from scratch.

# Reading GEXF files

The `rgexf` package comes with a network from Les Misérables, which is featured in Gephi. To read GEXF files, we can use the `read.gexf` function:

    # Loading rgexf
    library(rgexf)

    # Accessing the path of the file
    fn    <- system.file(
      "gexf-graphs/lesmiserables.gexf", package = "rgexf"
      )
    lesmi <- read.gexf(fn)

    # Taking a look at the first handful of nodes and edges
    head(lesmi)

    ## <?xml version="1.0" encoding="UTF-8"?>
    ## <gexf xmlns="http://www.gexf.net/1.3" xmlns:viz="http://www.gexf.net/1.3/viz" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.3" xsi:schemaLocation="http://www.gexf.net/1.3 http://www.gexf.net/1.3/gexf.xsd">
    ##   <meta lastmodifieddate="2016-11-09">
    ##     <creator>Gephi 0.9</creator>
    ##     <description/>
    ##   </meta>
    ##   <graph defaultedgetype="undirected" mode="static">
    ##     <attributes class="node" mode="static">
    ##       <attribute id="modularity_class" title="Modularity Class" type="integer"/>
    ##     </attributes>
    ##     <nodes>
    ##       <node id="11" label="Valjean">
    ##         <attvalues>
    ##           <attvalue for="modularity_class" value="1"/>
    ##         </attvalues>
    ##         <viz:size value="100.0"/>
    ##         <viz:position x="-87.93029" y="6.8120565"/>
    ##         <viz:color r="245" g="91" b="91"/>
    ##       </node>
    ##       <node id="48" label="Gavroche">
    ##         <attvalues>
    ##           <attvalue for="modularity_class" value="8"/>
    ##         </attvalues>
    ##         <viz:size value="61.600006"/>
    ##         <viz:position x="387.89572" y="-110.462326"/>
    ##         <viz:color r="91" g="245" b="91"/>
    ##       </node>
    ##       <node id="55" label="Marius">
    ##         <attvalues>
    ##           <attvalue for="modularity_class" value="6"/>
    ##         </attvalues>
    ##         <viz:size value="53.37143"/>
    ##         <viz:position x="206.44687" y="13.805411"/>
    ##         <viz:color r="194" g="91" b="245"/>
    ##       </node>
    ##       <node id="27" label="Javert">
    ##         <attvalues>
    ##           <attvalue for="modularity_class" value="7"/>
    ##         </attvalues>
    ##         <viz:size value="47.88571"/>
    ##         <viz:position x="-81.46074" y="204.20204"/>
    ##         <viz:color r="91" g="245" b="194"/>
    ##       </node>
    ##       <node id="25" label="Thenardier">
    ##         <attvalues>
    ##           <attvalue for="modularity_class" value="7"/>
    ##         </attvalues>
    ##         <viz:size value="45.142853"/>
    ##         <viz:position x="82.80825" y="203.1144"/>
    ##         <viz:color r="91" g="245" b="194"/>
    ##       </node>
    ##       <node id="23" label="Fantine">
    ##         <attvalues>
    ##           <attvalue for="modularity_class" value="2"/>
    ##         </attvalues>
    ##         <viz:size value="42.4"/>
    ##         <viz:position x="-313.42786" y="289.44803"/>
    ##         <viz:color r="91" g="194" b="245"/>
    ##       </node>
    ##          ...
    ##      </nodes>
    ##     <edges>
    ##       <edge id="0" source="1" target="0"/>
    ##       <edge id="1" source="2" target="0" weight="8.0"/>
    ##       <edge id="2" source="3" target="0" weight="10.0"/>
    ##       <edge id="3" source="3" target="2" weight="6.0"/>
    ##       <edge id="4" source="4" target="0"/>
    ##       <edge id="5" source="5" target="0"/>
    ##          ...
    ##      </edges>
    ##   </graph>
    ## </gexf>

Moreover, we can directly plot the graph using the `plot.gexf` method–through the `gexf-js` library–or coercing it into an `igraph` object and use igraph’s plotting engine:

    lesmi_ig <- gexf.to.igraph(lesmi)
    lesmi_ig

    ## IGRAPH debded4 UNW- 77 254 --
    ## + attr: layout (g/n), name (v/c), color (v/c), size (v/n), weight (e/n)
    ## + edges from debded4 (vertex names):
    ##  [1] Myriel        --Napoleon       Myriel        --MlleBaptistine
    ##  [3] Myriel        --MmeMagloire    MlleBaptistine--MmeMagloire
    ##  [5] Myriel        --CountessDeLo   Myriel        --Geborand
    ##  [7] Myriel        --Champtercier   Myriel        --Cravatte
    ##  [9] Myriel        --Count          Myriel        --OldMan
    ## [11] Myriel        --Valjean        Valjean       --MlleBaptistine
    ## [13] Valjean       --MmeMagloire    Labarre       --Valjean
    ## [15] Valjean       --Marguerite     Valjean       --MmeDeR
    ## + ... omitted several edges

    op <- par(mai = rep(0, 4)) # For extra space
    plot(lesmi_ig)

    par(op)

We can also go back:

    head(igraph.to.gexf(lesmi_ig))

    ## <?xml version="1.0" encoding="UTF-8"?>
    ## <gexf xmlns="http://www.gexf.net/1.3" xmlns:viz="http://www.gexf.net/1.3/viz" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.gexf.net/1.3 http://www.gexf.net/1.3/gexf.xsd" version="1.3">
    ##   <meta lastmodifieddate="2024-06-30">
    ##     <creator>NodosChile</creator>
    ##     <description>A GEXF file written in R with "rgexf"</description>
    ##     <keywords>GEXF, NodosChile, R, rgexf, Gephi</keywords>
    ##   </meta>
    ##   <graph mode="static" defaultedgetype="undirected">
    ##     <nodes>
    ##       <node id="Myriel" label="Myriel">
    ##         <viz:color r="91" g="91" b="245" a="1"/>
    ##         <viz:position x="-148.379397464743" y="-140.395409747888" z="0"/>
    ##         <viz:size value="1.86270876623377"/>
    ##       </node>
    ##       <node id="Napoleon" label="Napoleon">
    ##         <viz:color r="91" g="91" b="245" a="1"/>
    ##         <viz:position x="-209.928377825858" y="-212.835089666009" z="0"/>
    ##         <viz:size value="0.25974025974026"/>
    ##       </node>
    ##       <node id="Labarre" label="Labarre">
    ##         <viz:color r="245" g="91" b="91" a="1"/>
    ##         <viz:position x="-76.1564912097887" y="-108.343126644676" z="0"/>
    ##         <viz:size value="0.25974025974026"/>
    ##       </node>
    ##       <node id="Valjean" label="Valjean">
    ##         <viz:color r="245" g="91" b="91" a="1"/>
    ##         <viz:position x="-75.5824164344556" y="10.4450055312959" z="0"/>
    ##         <viz:size value="6.49350649350649"/>
    ##       </node>
    ##       <node id="Marguerite" label="Marguerite">
    ##         <viz:color r="245" g="91" b="91" a="1"/>
    ##         <viz:position x="-178.064757789707" y="97.9855519958049" z="0"/>
    ##         <viz:size value="0.437847987012987"/>
    ##       </node>
    ##       <node id="MmeDeR" label="MmeDeR">
    ##         <viz:color r="245" g="91" b="91" a="1"/>
    ##         <viz:position x="-118.871735089594" y="-80.7795279631479" z="0"/>
    ##         <viz:size value="0.25974025974026"/>
    ##       </node>
    ##          ...
    ##      </nodes>
    ##     <edges>
    ##       <edge id="0" source="Myriel" target="Napoleon" weight="1"/>
    ##       <edge id="1" source="Myriel" target="MlleBaptistine" weight="8"/>
    ##       <edge id="2" source="Myriel" target="MmeMagloire" weight="10"/>
    ##       <edge id="3" source="MlleBaptistine" target="MmeMagloire" weight="6"/>
    ##       <edge id="4" source="Myriel" target="CountessDeLo" weight="1"/>
    ##       <edge id="5" source="Myriel" target="Geborand" weight="1"/>
    ##          ...
    ##      </edges>
    ##   </graph>
    ## </gexf>

Using the `plot.gexf` method–which uses the `gexf-js` JavaScript library–results in a Web visualization of the graph, like this:

    plot(g)

An live version of the figure is available here.

# Creating GEXF files

This example was extracted directly from the demo “gexfrandom.” Here we create three networks with the same set of vertices and layout, we color them and finalize plotting it with igraph.

    # Random graph demo
    set.seed(11)

Creating the vertices:

    # Vertex
    n <- 30
    prb <- .3
    vertex1 <- data.frame(id = 1:n, label = 1:n)
    vertex2 <- data.frame(id = (n + 1):(2 * n), label = (n + 1):(2 * n))
    vertex3 <- data.frame(
      id = (2 * n + 1):(3 * n), label = (2 * n + 1):(3 * n)
      )

Building edges:

    # Edges
    edges1 <- combn(vertex1$label, 2)
    edges1 <- edges1[, which(runif(ncol(edges1)) > (1 - prb))]
    edges1 <- data.frame(source = edges1[1, ], target = edges1[2, ])

    edges2 <- combn(vertex2$label, 2)
    edges2 <- edges2[, which(runif(ncol(edges2)) > (1 - prb))]
    edges2 <- data.frame(source = edges2[1, ], target = edges2[2, ])

    edges3 <- combn(vertex3$label, 2)
    edges3 <- edges3[, which(runif(ncol(edges3)) > (1 - prb))]
    edges3 <- data.frame(source = edges3[1, ], target = edges3[2, ])

We can and add visual attributes:

    # Visual attributes
    size <- runif(n, max = 100)
    color <- terrain.colors(n)
    color <- color[order(runif(n))][1:n]
    color <- cbind(t(col2rgb(color)), 1)

    color2 <- heat.colors(n)
    color2 <- color2[order(runif(n))][1:n]
    color2 <- cbind(t(col2rgb(color2)), 1)

    color3 <- topo.colors(n)
    color3 <- color3[order(runif(n))][1:n]
    color3 <- cbind(t(col2rgb(color3)), 1)

Generating a layout:

    # Nice layout
    pos <- matrix(0, nrow = n, ncol = 3)

    for (i in 2:n) {
      pos[i, 1] <- pos[i - 1, 1] + cos(2 * pi * (i * 1.7 - 1) / n)
      pos[i, 2] <- pos[i - 1, 2] + sin(2 * pi * (i - 1) / n)
    }

    pos <- pos / (max(pos) - min(pos))
    pos2 <- pos
    pos2[, 1] <- pos2[, 1] + max(pos2[, 1]) - min(pos[, 1])
    pos3 <- pos
    pos3[, 1] <- pos3[, 1] + max(pos2[, 1]) - min(pos[, 1])

And finally, we can build the `gexf` object:

    graph <- gexf(
      rbind(vertex1, vertex2, vertex3),
      rbind(edges1, edges2, edges3),
      nodesVizAtt = list(
        size = c(size, size, size),
        color = rbind(color, color2, color3),
        position = rbind(pos, pos2, pos3)
      )
    )

    # Taking a quick look
    head(graph)

    ## <?xml version="1.0" encoding="UTF-8"?>
    ## <gexf xmlns="http://www.gexf.net/1.3" xmlns:viz="http://www.gexf.net/1.3/viz" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.gexf.net/1.3 http://www.gexf.net/1.3/gexf.xsd" version="1.3">
    ##   <meta lastmodifieddate="2024-06-30">
    ##     <creator>NodosChile</creator>
    ##     <description>A GEXF file written in R with "rgexf"</description>
    ##     <keywords>GEXF, NodosChile, R, rgexf, Gephi</keywords>
    ##   </meta>
    ##   <graph mode="static" defaultedgetype="undirected">
    ##     <nodes>
    ##       <node id="1" label="1">
    ##         <viz:color r="233" g="187" b="62" a="1"/>
    ##         <viz:position x="-140.199919726949" y="-250" z="0"/>
    ##         <viz:size value="5.55555555555556"/>
    ##       </node>
    ##       <node id="2" label="2">
    ##         <viz:color r="235" g="178" b="94" a="1"/>
    ##         <viz:position x="-114.232657063944" y="-239.073800366903" z="0"/>
    ##         <viz:size value="2.75415710515231"/>
    ##       </node>
    ##       <node id="3" label="3">
    ##         <viz:color r="242" g="242" b="242" a="1"/>
    ##         <viz:position x="-94.8700927475552" y="-217.698928454398" z="0"/>
    ##         <viz:size value="0.187776451016345"/>
    ##       </node>
    ##       <node id="4" label="4">
    ##         <viz:color r="240" g="201" b="192" a="1"/>
    ##         <viz:position x="-84.540989802301" y="-186.809568733076" z="0"/>
    ##         <viz:size value="3.05941177828193"/>
    ##       </node>
    ##       <node id="5" label="5">
    ##         <viz:color r="151" g="211" b="0" a="1"/>
    ##         <viz:position x="-84.540989802301" y="-147.755734446353" z="0"/>
    ##         <viz:size value="1.90801670817263"/>
    ##       </node>
    ##       <node id="6" label="6">
    ##         <viz:color r="232" g="195" b="46" a="1"/>
    ##         <viz:position x="-94.8700927475552" y="-102.244265553647" z="0"/>
    ##         <viz:size value="0.381918795494298"/>
    ##       </node>
    ##          ...
    ##      </nodes>
    ##     <edges>
    ##       <edge id="0" source="1" target="7" weight="1"/>
    ##       <edge id="1" source="1" target="10" weight="1"/>
    ##       <edge id="2" source="1" target="14" weight="1"/>
    ##       <edge id="3" source="1" target="15" weight="1"/>
    ##       <edge id="4" source="1" target="16" weight="1"/>
    ##       <edge id="5" source="2" target="8" weight="1"/>
    ##          ...
    ##      </edges>
    ##   </graph>
    ## </gexf>

As before, we can either directly call the plot function for `gexf` objects, or coerce it into an `igraph` object:

    # plot(graph)
    op <- par(mai = rep(0, 4)) # For extra space
    plot(gexf.to.igraph(graph))

    par(op)