symlog_trans: Scale positive and negative values on a log scale

In LightLogR: Process Data from Wearable Light Loggers and Optical Radiation Dosimeters

Scale positive and negative values on a log scale

Description

To create a plot with positive and negative (unscaled) values on a log-transformed axis, the values need to be scaled accordingly. R or ggplot2 do not have a built-in function for this, but the following function can be used to create a transformation function for this purpose. The function was coded based on a post on stack overflow. The symlog transformation is the standard transformation used e.g., in gg_day().

Usage

symlog_trans(base = 10, thr = 1, scale = 1)

Arguments

base	Base for the logarithmic transformation. The default is 10.
thr	Threshold after which a logarithmic transformation is applied. If the absolute value is below this threshold, the value is not transformed. The default is 1.
scale	Scaling factor for logarithmically transformed values above the threshold. The default is 1.

Details

The symlog transformation can be accessed either via the trans = "symlog" argument in a scaling function, or via trans = symlog_trans(). The latter allows setting the individual arguments.

Value

a transformation function that can be used in ggplot2 or plotly to scale positive and negative values on a log scale.

References

This function's code is a straight copy from a post on stack overflow. The author of the answer is Julius Vainora, and the author of the question Brian B

Examples

dataset <- 
sample.data.environment %>%
filter_Date(end = "2023-08-29") %>% 
dplyr::mutate(MEDI = dplyr::case_when(
                                     Id == "Environment" ~ -MEDI,
                                     .default = MEDI))
#basic application where transformation, breaks and labels are set manually
dataset %>%                                     
gg_day(aes_col = Id) +
ggplot2::scale_y_continuous(
trans = "symlog")

#the same plot, but with breaks and labels set manually                            
dataset %>%                                     
gg_day(aes_col = Id) +
ggplot2::scale_y_continuous(
trans = "symlog", 
breaks = c(-10^(5:0), 0, 10^(0:5)),
labels = function(x) format(x, scientific = FALSE, big.mark = " "))

#setting individual arguments of the symlog function manually allows
#e.g., to emphasize values smaller than 1
dataset %>%                                     
gg_day(aes_col = Id) +
ggplot2::scale_y_continuous(
trans = symlog_trans(thr = 0.01),
breaks = c(-10^(5:-1), 0, 10^(-1:5)),
labels = function(x) format(x, scientific = FALSE, big.mark = " "))

LightLogR documentation built on April 3, 2025, 10:10 p.m.