library(Rgraphviz)

# Assumes that a graph is  a data frame with columns
# subject, object, [label, width, hue, saturation, brightness]

namedvector <- function(names, values) {names(values) = names; values}

render <- function(graph) {
  nodes = union(graph$subject, graph$object)
  edges = tapply(graph$object, graph$subject, function(x) list(edges=as.character(x)), simplify=F)
  # add edges for object-only nodes (leafs)
  for (leaf in setdiff(graph$object, graph$subject)) edges[[leaf]] = list(edges=NULL)
  # create graph
  g <- new("graphNEL", nodes = nodes, edgeL = edges, edgemode="directed")
  # add labels, width, color if given
  edgeids = paste(graph$subject, graph$object, sep="~")
  edgeAttrs = if (is.null(graph$label)) list() else
    list(label=namedvector(edgeids, as.character(graph$label)) )
  if (!is.null(graph$col))
    edgeRenderInfo(g) <- list(col=namedvector(edgeids, as.character(graph$col)))
  if (!is.null(graph$width))
    edgeRenderInfo(g) <-  list(lwd=namedvector(edgeids, graph$width))
  if (!is.null(graph$label))
    edgeRenderInfo(g) <- list(label=namedvector(edgeids, as.character(graph$label)))
  # layour and render
  g = layoutGraph(g, recipEdges="distinct", edgeAttrs=edgeAttrs)
  renderGraph(g)
}

# test code: create normal and reciprocal graph and some attributes
graph = data.frame(subject=c("a", "c"), object=c("a", "a"))
rgraph = data.frame(subject=c("a", "b"), object=c("b", "a"))
label=c("0.7","-1.0")
col=c("blue","red")
width=c(2,4)

# plot graphs in rows with increasing #features complexity in columns
layout(matrix(1:8, nrow=2, byrow=T))
for (g in list(graph, rgraph)) {
  render(g)
  render(cbind(g, label=label))
  render(cbind(g, label=label, width=width))
  render(cbind(g, label=label, width=width, col=col))
}
# result at http://imageshack.us/photo/my-images/405/recip.png/