Wilkinson's labeling algorithm
Wilkinson's labeling algorithm
wilkinson(dmin, dmax, m,
Q = c(1, 5, 2, 2.5, 3, 4, 1.5, 7, 6, 8, 9),
mincoverage = 0.8,
mrange = max(floor(m/2), 2):ceiling(6 * m))dmin |
minimum of the data range |
dmax |
maximum of the data range |
m |
number of axis labels |
Q |
set of nice numbers |
mincoverage |
minimum ratio between the the data range and the labeling range, controlling the whitespace around the labeling (default = 0.8) |
mrange |
range of |
vector of axis label locations
Ported from Wilkinson's Java implementation with some changes. Changes: 1) m (the target number of ticks) is hard coded in Wilkinson's implementation as 5. Here we allow it to vary as a parameter. Since m is fixed, Wilkinson only searches over a fixed range 4-13 of possible resulting ticks. We broadened the search range to max(floor(m/2),2) to ceiling(6*m), which is a larger range than Wilkinson considers for 5 and allows us to vary m, including using non-integer values of m. 2) Wilkinson's implementation assumes that the scores are non-negative. But, his revised granularity function can be extremely negative. We tweaked the code to allow negative scores. We found that this produced better labelings. 3) We added 10 to Q. This seemed to be necessary to get steps of size 1. It is possible for this algorithm to find no solution. In Wilkinson's implementation, instead of failing, he returns the non-nice labels spaced evenly from min to max. We want to detect this case, so we return NULL. If this happens, the search range, mrange, needs to be increased.
Justin Talbot justintalbot@gmail.com
Wilkinson, L. (2005) The Grammar of Graphics, Springer-Verlag New York, Inc.
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