An example how to use R and rgexf package to create a .gexf file for network visualization in Gephi

plotNetworksUsingGephi.R

# Plotting networks in R 
# An example how to use R and rgexf package to create a .gexf file for network visualization in Gephi

############################################################################################
# Clear workspace 
rm(list = ls())

# Load libraries
library("igraph")
library("plyr")

# Read a data set. 
# Data format: dataframe with 3 variables; variables 1 & 2 correspond to interactions; variable 3 corresponds to the weight of interaction
dataSet <- read.table("lesmis.txt", header = FALSE, sep = "\t")

# Create a graph. Use simplify to ensure that there are no duplicated edges or self loops
gD <- simplify(graph.data.frame(dataSet, directed=FALSE))

# Print number of nodes and edges
# vcount(gD)
# ecount(gD)

############################################################################################
# Calculate some node properties and node similarities that will be used to illustrate 
# different plotting abilities

# Calculate degree for all nodes
degAll <- degree(gD, v = V(gD), mode = "all")

# Calculate betweenness for all nodes
betAll <- betweenness(gD, v = V(gD), directed = FALSE) / (((vcount(gD) - 1) * (vcount(gD)-2)) / 2)
betAll.norm <- (betAll - min(betAll))/(max(betAll) - min(betAll))
rm(betAll)

# Calculate Dice similarities between all pairs of nodes
dsAll <- similarity.dice(gD, vids = V(gD), mode = "all")

############################################################################################
# Add new node/edge attributes based on the calculated node properties/similarities

gD <- set.vertex.attribute(gD, "degree", index = V(gD), value = degAll)
gD <- set.vertex.attribute(gD, "betweenness", index = V(gD), value = betAll.norm)

# Check the attributes
# summary(gD)

F1 <- function(x) {data.frame(V4 = dsAll[which(V(gD)$name == as.character(x$V1)), which(V(gD)$name == as.character(x$V2))])}
dataSet.ext <- ddply(dataSet, .variables=c("V1", "V2", "V3"), function(x) data.frame(F1(x)))

gD <- set.edge.attribute(gD, "weight", index = E(gD), value = 0)
gD <- set.edge.attribute(gD, "similarity", index = E(gD), value = 0)

# The order of interactions in gD is not the same as it is in dataSet or as it is in the edge list,
# and for that reason these values cannot be assigned directly

E(gD)[as.character(dataSet.ext$V1) %--% as.character(dataSet.ext$V2)]$weight <- as.numeric(dataSet.ext$V3)
E(gD)[as.character(dataSet.ext$V1) %--% as.character(dataSet.ext$V2)]$similarity <- as.numeric(dataSet.ext$V4)


# Check the attributes
# summary(gD)

####################################
# Print network in the file format ready for Gephi
# This requires rgexf package

library("rgexf")

# Create a dataframe nodes: 1st column - node ID, 2nd column -node name
nodes_df <- data.frame(ID = c(1:vcount(gD)), NAME = V(gD)$name)
# Create a dataframe edges: 1st column - source node ID, 2nd column -target node ID
edges_df <- as.data.frame(get.edges(gD, c(1:ecount(gD))))

# Define node and edge attributes - these attributes won't be directly used for network visualization, but they
# may be useful for other network manipulations in Gephi
#
# Create a dataframe with node attributes: 1st column - attribute 1 (degree), 2nd column - attribute 2 (betweenness)
nodes_att <- data.frame(DEG = V(gD)$degree, BET = V(gD)$betweenness) 
#
# Create a dataframe with edge attributes: 1st column - attribute 1 (weight), 2nd column - attribute 2 (similarity)
edges_att <- data.frame(WGH = E(gD)$weight, SIM = E(gD)$similarity) 

# Define node/edge visual attributes - these attributes are the ones used for network visualization
#
# Calculate node coordinate - needs to be 3D
#nodes_coord <- as.data.frame(layout.fruchterman.reingold(gD, weights = E(gD)$similarity, dim = 3, niter = 10000))
# We'll cheat here, as 2D coordinates result in a better (2D) plot than 3D coordinates
nodes_coord <- as.data.frame(layout.fruchterman.reingold(gD, weights = E(gD)$similarity, dim = 2, niter = 10000))
nodes_coord <- cbind(nodes_coord, rep(0, times = nrow(nodes_coord)))
#
# Calculate node size
# We'll interpolate node size based on the node betweenness centrality, using the "approx" function
approxVals <- approx(c(1, 5), n = length(unique(V(gD)$betweenness)))
# And we will assign a node size for each node based on its betweenness centrality
nodes_size <- sapply(V(gD)$betweenness, function(x) approxVals$y[which(sort(unique(V(gD)$betweenness)) == x)])
#
# Define node color
# We'll interpolate node colors based on the node degree using the "colorRampPalette" function from the "grDevices" library
library("grDevices")
# This function returns a function corresponding to a collor palete of "bias" number of elements
F2 <- colorRampPalette(c("#F5DEB3", "#FF0000"), bias = length(unique(V(gD)$degree)), space = "rgb", interpolate = "linear")
# Now we'll create a color for each degree
colCodes <- F2(length(unique(V(gD)$degree)))
# And we will assign a color for each node based on its degree
nodes_col <- sapply(V(gD)$degree, function(x) colCodes[which(sort(unique(V(gD)$degree)) == x)])
# Transform it into a data frame (we have to transpose it first)
nodes_col_df <- as.data.frame(t(col2rgb(nodes_col, alpha = FALSE)))
# And add alpha (between 0 and 1). The alpha from "col2rgb" function takes values from 0-255, so we cannot use it
nodes_col_df <- cbind(nodes_col_df, alpha = rep(1, times = nrow(nodes_col_df)))
# Assign visual attributes to nodes (colors have to be 4dimensional - RGBA)
nodes_att_viz <- list(color = nodes_col_df, position = nodes_coord, size = nodes_size)

# Assign visual attributes to edges using the same approach as we did for nodes
F2 <- colorRampPalette(c("#FFFF00", "#006400"), bias = length(unique(E(gD)$weight)), space = "rgb", interpolate = "linear")
colCodes <- F2(length(unique(E(gD)$weight)))
edges_col <- sapply(E(gD)$weight, function(x) colCodes[which(sort(unique(E(gD)$weight)) == x)])
edges_col_df <- as.data.frame(t(col2rgb(edges_col, alpha = FALSE)))
edges_col_df <- cbind(edges_col_df, alpha = rep(1, times = nrow(edges_col_df)))
edges_att_viz <-list(color = edges_col_df)

# Write the network into a gexf (Gephi) file
#write.gexf(nodes = nodes_df, edges = edges_df, nodesAtt = nodes_att, edgesWeight = E(gD)$weight, edgesAtt = edges_att, nodesVizAtt = nodes_att_viz, edgesVizAtt = edges_att_viz, defaultedgetype = "undirected", output = "lesmis.gexf")
# And without edge weights
write.gexf(nodes = nodes_df, edges = edges_df, nodesAtt = nodes_att, edgesAtt = edges_att, nodesVizAtt = nodes_att_viz, edgesVizAtt = edges_att_viz, defaultedgetype = "undirected", output = "lesmis.gexf")

It sounds like an error related to creating an xml file, which the gexf file is. However, I just ran the code and didn't get any errors. Which R and package versions are you using?

Here is my session info, if it helps

> print(sessionInfo())
R version 3.2.3 (2015-12-10)
Platform: x86_64-redhat-linux-gnu (64-bit)
Running under: Fedora 23 (Workstation Edition)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8     LC_MONETARY=en_US.UTF-8   
 [6] LC_MESSAGES=en_US.UTF-8    LC_PAPER=en_US.UTF-8       LC_NAME=C                  LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] rgexf_0.15.3    Rook_1.1-1      XML_3.98-1.4    igraph_1.0.1    plyr_1.8.3.9000

loaded via a namespace (and not attached):
[1] magrittr_1.5      rsconnect_0.4.2.2 tools_3.2.3       Rcpp_0.12.4       brew_1.0-6    

Hi, how to find the file lesmis.txt?

Here: https://gist.github.com/Vessy/6c9567f26f397320ae849445ac92a981#file-lesmis-txt or http://www.vesnam.com/Rblog/wp-content/uploads/2013/07/lesmis.txt

The network is originally from D. E. Knuth, The Stanford GraphBase: A Platform for Combinatorial Computing, Addison-Wesley, Reading, MA, 1993.