Dynamically select a good bin width for a dotplot

Source: R/binning_methods.R

Searches for a nice-looking bin width to use to draw a dotplot such that the height of the dotplot fits within a given space (maxheight).

find_dotplot_binwidth(x, maxheight, heightratio = 1, stackratio = 1)

Arguments

x

numeric vector of values

maxheight

maximum height of the dotplot

heightratio

ratio of bin width to dot height

stackratio

ratio of dot height to vertical distance between dot centers

Value

A suitable bin width such that a dotplot created with this bin width and heightratio should have its tallest bin be less than or equal to maxheight.

Details

This dynamic bin selection algorithm uses a binary search over the number of bins to find a bin width such that if the input data (x) is binned using a Wilkinson-style dotplot algorithm the height of the tallest bin will be less than maxheight.

This algorithm is used by geom_dotsinterval() (and its variants) to automatically select bin widths. Unless you are manually implementing you own dotplot grob or geom, you probably do not need to use this function directly

See also

bin_dots() for an algorithm can bin dots using bin widths selected by this function; geom_dotsinterval() for geometries that use these algorithms to create dotplots.

Examples


library(dplyr)
library(ggplot2)

x = qnorm(ppoints(20))
binwidth = find_dotplot_binwidth(x, maxheight = 4, heightratio = 1)
binwidth
#> [1] 0.6533213

bin_df = bin_dots(x = x, y = 0, binwidth = binwidth, heightratio = 1)
bin_df
#> # A tibble: 20 x 3
#>         x     y   bin
#>     <dbl> <dbl> <dbl>
#>  1 -1.70  0.327     1
#>  2 -1.70  0.980     1
#>  3 -0.984 0.327     2
#>  4 -0.984 0.980     2
#>  5 -0.984 1.63      2
#>  6 -0.330 0.327     3
#>  7 -0.330 0.980     3
#>  8 -0.330 1.63      3
#>  9 -0.330 2.29      3
#> 10 -0.330 2.94      3
#> 11  0.330 0.327     4
#> 12  0.330 0.980     4
#> 13  0.330 1.63      4
#> 14  0.330 2.29      4
#> 15  0.330 2.94      4
#> 16  0.984 0.327     5
#> 17  0.984 0.980     5
#> 18  0.984 1.63      5
#> 19  1.70  0.327     6
#> 20  1.70  0.980     6

# we can manually plot the binning above, though this is only recommended
# if you are using find_dotplot_binwidth() and bin_dots() to build your own
# grob. For practical use it is much easier to use geom_dots(), which will
# automatically select good bin widths for you (and which uses
# find_dotplot_binwidth() and bin_dots() internally)
bin_df %>%
  ggplot(aes(x = x, y = y)) +
  geom_point(size = 4) +
  coord_fixed()