halfcircle {halfcircle}

Visualization method for flow data using halfcircle diagram

Description

halfcircle function draws flows between nodes creating halfcircle diagram.

Usage

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)

Arguments

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

Details

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.

Author(s)

Sohyun Park <[e-mail]>, Ningchuan Xiao

References

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

Examples

# 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)