Scale a color palette centered on zero

center_palette.R

# Scale a color palette centered on zero

#' Get the lower, upper, or absolute maximum value
#' of a variable in a dataframe
#' 
#' For setting plotting limits manually
#'
#' @param data Dataframe
#' @param var Name of variable (column) in dataframe
#' @param digits Number of digits desired in output
#' @param type Type of limit to calculate: "min" is lower,
#' "max" is upper, and "abs" is the absolute greatest value.
#'
#' @return Number
#'
#' @examples
#' get_limit(mtcars, disp, "max")
get_limit <- function (data, var, type = c("min", "max", "abs"), digits = 2) {
  
  var <- rlang::enquo(var)
  
  switch(type,
         
         max = data %>% 
           dplyr::pull(!!var) %>% 
           max(na.rm = TRUE) %>% 
           magrittr::multiply_by(10^digits) %>% ceiling %>% magrittr::divide_by(10^digits),
         
         min = data %>% 
           pull(!!var) %>% 
           min(na.rm = TRUE) %>% 
           magrittr::multiply_by(10^digits) %>% floor %>% magrittr::divide_by(10^digits),
         
         abs = c(
           data %>% dplyr::pull(!!var) %>% max(na.rm = TRUE),
           data %>% dplyr::pull(!!var) %>% min(na.rm = TRUE)) %>% 
           abs %>% max %>%
           magrittr::multiply_by(10^digits) %>% ceiling %>% magrittr::divide_by(10^digits)
  )
  
}

library(tidyverse)
library(scico)

data <- tibble(
  intensity = rnorm(10),
  xpos = 1:10,
  ypos = 1:10
)

# Color will be centered on zero regardless of values of `intensity` in the dataframe
ggplot (data, aes(x = xpos, y = ypos, color = intensity)) +
  geom_point() +
scale_color_scico(
  palette = "vik", 
  na.value="dark grey",
  limits = c(
    -get_limit(data, intensity, "abs", 3), 
    get_limit(data, intensity, "abs", 3)
  ))