```
# gGtools.R
#
# Utility functions for gG objects
.df2gG <- function(netDF, isDirected = TRUE, simplify = TRUE) {
# Purpose:
# Creates a gG object from the dataframe netDF
#
# Parameters:
# netDF: a dataframe with two columns of vertex IDs and one column
# of edge weights.
# isDirected: default TRUE - whether the data frame contains
# directed edges.
# simplify: default TRUE - whether or not to collapse multiple edges
# Details:
# igraph expects columns 1 and 2 of netDF to contain vertex names, the
# remaining columns to contain edge attributes. Edge attributes will get
# the name of the column they come from. If isDirected is true, absent
# edges are implied to have weight 0 but they are not explicitly added.
# If is Directed is false, igraph::as.directed() expands the graph to
# have directed edges. If simplify is true multiple edges and loops are
# collapsed and the max() of the weights is the attribute of the
# combined edge.
#
# gG objects are defined to be weighted, directed, simple graphs
# the parameters isDirected and simplify are provided merely for
# development purposes and should not be changed.
# Value:
# gG: igraph graph object with metadata attached as attributes
# ==== SETUP METADATA ======================================================
meta <- list(type = "gG",
version = "1.0",
UUID = uuid::UUIDgenerate())
# ==== CREATE IGRAPH GRAPH =================================================
if (isDirected) {
gG <- igraph::graph_from_data_frame(get("netDF", parent.frame()),
directed = TRUE)
} else {
gG <- igraph::graph_from_data_frame(get("netDF", parent.frame()),
directed = FALSE)
gG <- igraph::as.directed(gG, mode = "mutual")
}
# ==== SIMPLIFY GRAPH ======================================================
if (simplify) {
gG <- igraph::simplify(gG,
remove.multiple = TRUE,
remove.loops = TRUE,
edge.attr.comb = "max")
}
# ToDo - report if edges were simplified away since this
# may give us less than the requested number xN of edges.
# ==== ATTACH METADATA =====================================================
for (name in names(meta)) {
attr(gG, name) <- meta[[name]]
}
return(gG)
}
# [END]
```

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