The colorRamp2() function can generate a color mapping function from a vector of break values and a vector of corresponding colors. Other colors are linearly interpolated in a certain color space.
library(colorRamp2)
col_fun = colorRamp2(c(0, 0.5, 1), c("blue", "white", "red"))
col_fun(seq(0, 1, length = 20))## [1] "#0000FFFF" "#522CFFFF" "#7448FFFF" "#8E61FFFF" "#A479FFFF" "#B891FFFF"
## [7] "#C9A9FFFF" "#DAC1FFFF" "#E9DAFFFF" "#F8F3FFFF" "#FFF5F1FF" "#FFE1D6FF"
## [13] "#FFCDBBFF" "#FFB8A1FF" "#FFA388FF" "#FF8E6EFF" "#FF7756FF" "#FF5E3DFF"
## [19] "#FF3F23FF" "#FF0000FF"plot(NULL, xlim = c(0, 1), ylim = c(0, 1))
x = seq(0, 1, length = 20)
y = rep(0.5, 20)
points(x, y, pch = 16, col = col_fun(x), cex = 2)
With the color mapping function col_fun, colors can be mapped back to the original numeric values. Note since colors are discrete, the values that are mapped back are not exactly identical to their original values.
x1 = runif(10)
col = col_fun(x1)
x2 = col2value(col, col_fun = col_fun)
x1## [1] 0.7853539 0.3305331 0.9602919 0.7126902 0.6421130 0.2226382 0.6644241
## [8] 0.4527759 0.4884661 0.8601798x2## [1] 0.7725624 0.3340315 0.9582373 0.6980786 0.6288315 0.2268344 0.6504547
## [8] 0.4548796 0.4898490 0.8502995sessionInfo()## R version 4.2.0 (2022-04-22)
## Platform: x86_64-apple-darwin17.0 (64-bit)
## Running under: macOS Big Sur/Monterey 10.16
##
## Matrix products: default
## BLAS: /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRblas.0.dylib
## LAPACK: /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRlapack.dylib
##
## locale:
## [1] C/UTF-8/C/C/C/C
##
## attached base packages:
## [1] stats graphics grDevices utils datasets methods base
##
## other attached packages:
## [1] colorRamp2_0.1.0
##
## loaded via a namespace (and not attached):
## [1] digest_0.6.31 R6_2.5.1 lifecycle_1.0.3 jsonlite_1.8.4
## [5] magrittr_2.0.3 evaluate_0.19 highr_0.9 stringi_1.7.8
## [9] rlang_1.0.6 cachem_1.0.6 cli_3.4.1 jquerylib_0.1.4
## [13] bslib_0.4.2 vctrs_0.5.1 rmarkdown_2.19 tools_4.2.0
## [17] stringr_1.5.0 glue_1.6.2 xfun_0.35 yaml_2.3.6
## [21] fastmap_1.1.0 compiler_4.2.0 colorspace_2.0-3 htmltools_0.5.4
## [25] knitr_1.41 sass_0.4.4