spread.labs {TeachingDemos}

Spread out close points for labeling in plots

Description

This function takes as set of coordinates and spreads out the close values so that they can be used in labeling plots without overlapping.

Usage

spread.labs(x, mindiff, maxiter = 1000, stepsize = 1/10, min = -Inf, max = Inf)

Arguments

x

The coordinate values (x or y, not both) to spread out.

mindiff

The minimum distance between return values

maxiter

The maximum number of iterations

stepsize

How far to move values in each iteration

min

Minimum bound for returned values

max

Maximum bound for returned values

Details

Sometimes the desired locations for labels in plots results in the labels overlapping. This function takes the coordinate values (x or y, not both) and finds those points that are less than mindiff (usually a function of strheight or strwidth) apart and increases the space between them (by stepsize * mindiff). This may or may not be enough and moving some points away from their nearest neighbor may move them too close to another neighbor, so the process is iterated until either maxiter steps have been tried, or all the values are at least mindiff apart.

The min and max arguments prevent the values from going outside that range (they should be specified such that the original values are all inside the range).

The values do not need to be presorted.

Value

A vector of coordinates (order corresponding to the original x) that can be used as a replacement for x in placing labels.

Author(s)

Greg Snow, [e-mail]

See Also

text, the spread.labels function in the plotrix package.

Examples

# overlapping labels
plot(as.integer(state.region), state.x77[,1], ylab='Population',
	xlab='Region',xlim=c(1,4.75), xaxt='n')
axis(1, at=1:4, lab=levels(state.region) )

text( as.integer(state.region)+.5, state.x77[,1], state.abb )
segments( as.integer(state.region)+0.025, state.x77[,1],
		as.integer(state.region)+.375, state.x77[,1] )

# now lets redo the plot without overlap

tmp.y <- state.x77[,1]
for(i in levels(state.region) ) {
  tmp <- state.region == i
  tmp.y[ tmp ] <- spread.labs( tmp.y[ tmp ], 1.2*strheight('A'),
	maxiter=1000, min=0 )
}

plot(as.integer(state.region), state.x77[,1], ylab='Population',
	xlab='Region', xlim=c(1,4.75), xaxt='n')
axis(1, at=1:4, lab=levels(state.region) )

text( as.integer(state.region)+0.5, tmp.y, state.abb )
segments( as.integer(state.region)+0.025, state.x77[,1],
		as.integer(state.region)+0.375, tmp.y )