halfcircle: Visualization method for flow data using halfcircle diagram
In halfcircle: Plot Halfcircle Diagram

Description Usage Arguments Details Author(s) References Examples

View source: R/halfcircle.R

halfcircle function draws flows between nodes creating halfcircle diagram.

halfcircle(flow, node, dir = "horizontal", circle.col = "lightgray",
  circle.trans = 0.5, flow.col = "black", flow.trans = 0.5,
  flow.width = "proportional", node.color = "black", node.size = 0.1,
  node.pch = 20, node.trans = 0.7, label = node[, c(1)],
  label.size = 0.5, label.col = "black", label.gap = 0.1)

`flow`	a dataframe which is to draw half-circles. The data should be in the form of an edge list containing node of origin, node of destination, and magnitude of the flow on the first three columns.
`node`	a dataframe which contains names of node on the first column. Nodes on the center line of a circle are drawn by the order of the data. Every node presented in flow data must be contained.
`dir`	if 'horizontal' (the default), nodes are drawn along the X-axis. If 'vertical', nodes are drawn along the Y-axis.
`circle.col`	color of background circle
`circle.trans`	transparency of color of background circle
`flow.col`	flow color. flow.col can be a list of color vectors, the vectors are then used per flow.
`flow.trans`	transparency of color of flows
`flow.width`	width of flows. if 'proportional' (the default), each width is calculated to be proportional to the maximum volume of flows. Maximum width is set to be 10. Otherwise, a list of width vectors can be used per flow.
`node.color`	node color. It can be a list of color vectors, and the vectors are then used per node.
`node.size`	node size
`node.pch`	node type. see ?points for more options.
`node.trans`	transparency of color of flows
`label`	the first column of node, names, is represented (the default). a list of vector an be used per node. if NULL, no label is drawn.
`label.size`	label size
`label.col`	label color
`label.gap`	gap between the node and the respective label

This function is a low-level graphical function, and you will create a halfcircle diagram. To create the diagram, nodes are placed as a set of points on a straight line segment in the center of a circle. The flow between two nodes is represented using a half cicle drawn from the origin to the destination in a clockwise direction. It is virtually drawn on xy-coordinates where both x and y range from -1 to 1. Flows between the same nodes are not drawn.

Sohyun Park <park.2627@osu.edu>, Ningchuan Xiao

Xiao and Chun (2009) <doi:10.1559/152304009788188763>

# load flow data
data(ex_flow)
flow <- ex_flow[,c(1,2,3)] # select veget column as volume
flow <- subset(flow,flow$vegetable>5000)
data(ex_node) # load node data
node <- ex_node[c(order(-ex_node$gdpc)),] # sort nodes in descending order of gdpc values
halfcircle(flow, node, dir="vertical", circle.col="gray", flow.col="black",label=NULL)

# legend
max <- max(flow[,c(3)]); median <- median(flow[,c(3)]); min <- min(flow[,c(3)])
max_w <- 10; median_w <- round(10*median/max); min_w <- round(10*min/max)
legend(x=-1.2, y=-0.8, legend=c(paste(round(max)), paste(round(median)), paste(round(min))),
    lty=1, lwd=c(max_w, median_w, min_w), cex=0.7)

# customize colors
node$color <- c("#22abcb","#4eb6ad","#86c388","#adcd6c","#dad84f")[node$income_level]
flow2 <- data.frame(flow, node[match(flow[,"O"], node[,"country"]),])
halfcircle(flow2, node, dir="vertical", flow.col=flow2$color, node.color=node$color, label=NULL)

# highlight one node
flow3 <- flow
flow3$color <- "gray"
flow3$color[flow3$O=="China"|flow3$D=="China"] <- "blue"
flow3 <- flow3[c(order(flow3$color,decreasing=TRUE)),]
node$label <- ""
node$label[node$country=="China"] <- "China"
halfcircle(flow3, node, dir="vertical", flow.col=flow3$color, label=node$label, label.size=0.7)