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.
## [1] 0.69702097 0.42804438 0.27354010 0.26592178 0.55438586 0.98395411
## [7] 0.97103453 0.06109919 0.32829228 0.49889222
## [1] 0.68241141 0.42982102 0.27745186 0.26856094 0.54806350 0.98302000
## [7] 0.96944771 0.06182574 0.33173620 0.49777512
## R version 4.4.1 (2024-06-14)
## Platform: x86_64-pc-linux-gnu
## Running under: Ubuntu 24.04.1 LTS
##
## Matrix products: default
## BLAS: /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3
## LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.26.so; LAPACK version 3.12.0
##
## locale:
## [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
## [3] LC_TIME=en_US.UTF-8 LC_COLLATE=C
## [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
## [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
## [9] LC_ADDRESS=C LC_TELEPHONE=C
## [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
##
## time zone: Etc/UTC
## tzcode source: system (glibc)
##
## attached base packages:
## [1] stats graphics grDevices utils datasets methods base
##
## other attached packages:
## [1] colorRamp2_0.0.1 rmarkdown_2.28
##
## loaded via a namespace (and not attached):
## [1] digest_0.6.37 R6_2.5.1 fastmap_1.2.0 xfun_0.47
## [5] maketools_1.3.0 cachem_1.1.0 knitr_1.48 htmltools_0.5.8.1
## [9] buildtools_1.0.0 lifecycle_1.0.4 cli_3.6.3 sass_0.4.9
## [13] jquerylib_0.1.4 compiler_4.4.1 highr_0.11 sys_3.4.2
## [17] tools_4.4.1 evaluate_0.24.0 bslib_0.8.0 colorspace_2.1-1
## [21] yaml_2.3.10 jsonlite_1.8.8 rlang_1.1.4