Functions for making breaks

Functions that return functions suitable to use as the breaks argument in ggplot2's continuous scales and in geom_contour_fill.

Modifies a breaks function to compute breaks using a trimmed range of the data to avoid extreme outliers stretching the scale.

Usage

MakeBreaks(binwidth = NULL, bins = 10, exclude = NULL)

AnchorBreaks(anchor = 0, binwidth = NULL, exclude = NULL, bins = 10)

robust_breaks(breaks = MakeBreaks(), quantiles = c(0.02, 0.98))

Arguments

binwidth

width of breaks

bins

number of bins, used if binwidth = NULL

exclude

a vector of breaks to exclude

anchor

anchor value

breaks

A function that takes the range of the data and binwidth as input and returns the the breaks as output.

quantiles

Numeric vector of length 2, sorted in ascending order, with values between 0 and 1 representing the quantiles of z that define the range used to compute breaks.

Value

A function that takes a range as argument and a binwidth as an optional argument and returns a sequence of equally spaced intervals covering the range. For robust_breaks, a function to use as breaks argument in contour geoms. It takes a data frame containing a column z, binwidth and bin arguments and returns a numeric vector of breaks, possibly including -Inf and Inf.

Details

MakeBreaks is essentially an export of the default way ggplot2::stat_contour makes breaks.

AnchorBreaks makes breaks starting from an anchor value and covering the range of the data according to binwidth.

See also

Other ggplot2 helpers: WrapCircular(), geom_arrow(), geom_contour2(), geom_contour_fill(), geom_label_contour(), geom_relief(), geom_streamline(), guide_colourstrip(), map_labels, reverselog_trans(), scale_divergent, scale_longitude, stat_na(), stat_subset()

Examples

my_breaks <- MakeBreaks(10)
my_breaks(c(1, 100))
#>  [1]   0  10  20  30  40  50  60  70  80  90 100
my_breaks(c(1, 100), 20)    # optional new binwidth argument ignored
#>  [1]   0  10  20  30  40  50  60  70  80  90 100

MakeBreaks()(c(1, 100), 20)  # but is not ignored if initial binwidth is NULL
#> [1]   0  20  40  60  80 100
# One to one mapping between contours and breaks
library(ggplot2)
binwidth <- 20
ggplot(reshape2::melt(volcano), aes(Var1, Var2, z = value)) +
    geom_contour(aes(color = after_stat(level)), binwidth = binwidth) +
    scale_color_continuous(breaks = MakeBreaks(binwidth))


#Two ways of getting the same contours. Better use the second one.
ggplot(reshape2::melt(volcano), aes(Var1, Var2, z = value)) +
    geom_contour2(aes(color = after_stat(level)), breaks = AnchorBreaks(132),
                  binwidth = binwidth) +
    geom_contour2(aes(color = after_stat(level)), breaks = AnchorBreaks(132, binwidth)) +
    scale_color_continuous(breaks = AnchorBreaks(132, binwidth))


# Sample data with extremes
surface <- reshape2::melt(volcano)
surface$value[sample(nrow(surface), 20)] <- 1000

# With regular breaks the outliers stretch the scale
# and prevent seeing the variability of the bulk of the data
ggplot(surface, aes(Var1, Var2, z = value)) +
  geom_contour_fill()


# Robust breaks removes those points from the break 
# computation and allow to see the variability
ggplot(surface, aes(Var1, Var2, z = value)) +
  geom_contour_fill(breaks = robust_breaks())