Pretty axis breaks inclusive of extreme values

This function returns pretty axis breaks that always include the extreme values of the data. This works by calling the extended Wilkinson algorithm (Talbot et al., 2010), constrained to solutions interior to the data range. Then, the minimum and maximum labels are moved to the minimum and maximum of the data range.

Usage

extended_range_breaks_(
  dmin,
  dmax,
  n = 5,
  Q = c(1, 5, 2, 2.5, 4, 3),
  w = c(0.25, 0.2, 0.5, 0.05)
)

extended_range_breaks(n = 5, ...)

Arguments

dmin: minimum of the data range
dmax: maximum of the data range
n: desired number of breaks
Q: set of nice numbers
w: weights applied to the four optimization components (simplicity, coverage, density, and legibility)
...: other arguments passed to extended_range_breaks_()

Value

For extended_range_breaks_, the vector of axis label locations. For extended_range_breaks, a function which takes a single argument, a vector of data, and returns the vector of axis label locations.

Details

extended_range_breaks_ implements the algorithm and returns the break values. extended_range_breaks uses the conventions of the scales package, and returns a function.

Note that ggplot2 hands a breaks function the expanded scale limits, not the data range. Passing extended_range_breaks() directly to breaks therefore places the end labels at the panel edges rather than at the extremes of the data. To label the extremes, which is what pairs with geom_rangeframe(), apply the function to the data instead: scale_x_continuous(breaks = extended_range_breaks()(mtcars$wt)).

References

Talbot, J., Lin, S., Hanrahan, P. (2010) An Extension of Wilkinson's Algorithm for Positioning Tick Labels on Axes, InfoVis 2010.

Author

Justin Talbot jtalbot@stanford.edu, Jeffrey B. Arnold, Baptiste Auguie