# [R] General means of matching a color specification to an official R color name

Bryan Hanson hanson at depauw.edu
Tue Oct 13 22:43:16 CEST 2009

```Hello List Dwellers:

I¹ve looked around quite a bit, but don¹t quite see an answer that I
understand.

I¹m looking for a way to take any kind of color specification (rgb, hsv,
hcl, hex) and match it to the n-nearest R official color names.  Clearly it
is easy to interconvert different specification schemes and color spaces,
but matching to the name seems a bit trickier.  Seems like if one has a
specification, it could be fuzzy-matched to the list of official R colors
expressed in the same specification.  Unfortunately, I don¹t know much about
fuzzy matching.

For example, following some examples I found in the archives and the wiki, I
wrote this little function to create a table of official R colors and sort
it if desired:

colorSpecTable <- function(col = colors(), sort = NULL){
require(gplots)
rgbcodes <- t(col2rgb(col))
names <- col
hex <- col2hex(col)
df <- data.frame(name = names, hex.code = hex, rgbcodes)
if (!identical(sort, NULL)) df <- sort.data.frame(df, by = sort)
}

Note that sort.data.frame is from the R-wiki and is appended below.  Is
there a clever way to search a table created by this function, and identify
the n-closest colors based upon some reasonable criteria?  What I hope for
is something like this:

colorMatch <- function(hex = NULL, n, plot = HOPEFULLY) {
df.rgb <- colorSpecTable(sort = ~red+green+blue) # master table
# now search for the n closest matches of hex in df.rgb\$hex.code
# perhaps hex should be converted into a different color space 1st
# eventually would like to display matches side by side w/hex
}

Thanks as always.  Bryan
*************
Bryan Hanson
Acting Chair
Professor of Chemistry & Biochemistry
DePauw University, Greencastle IN USA

sort.data.frame <- function(x, by){
# Author: Kevin Wright
# with some ideas from Andy Liaw
# Found in the R Wiki

# x: A data.frame
# by: A one-sided formula using + for ascending and - for descending
# Sorting is left to right in the formula

# Useage is:
# library(nlme);
# data(Oats)
# sort(Oats, by= ~nitro-Variety)

if(by[[1]] != "~")
stop("Argument 'by' must be a one-sided formula.")

# Make the formula into character and remove spaces
formc <- as.character(by[2])
formc <- gsub(" ", "", formc)
# If the first character is not + or -, add +
if(!is.element(substring(formc, 1, 1), c("+", "-")))
formc <- paste("+", formc, sep = "")

# Extract the variables from the formula
vars <- unlist(strsplit(formc, "[\\+\\-]"))
vars <- vars[vars != ""] # Remove any extra "" terms

# Build a list of arguments to pass to "order" function
calllist <- list()
pos <- 1 # Position of + or -
for(i in 1:length(vars)){
varsign <- substring(formc, pos, pos)
pos <- pos + 1 + nchar(vars[i])
if(is.factor(x[, vars[i]])){
if(varsign == "-") {
calllist[[i]] <- -rank(x[, vars[i]])
} else {
calllist[[i]] <- rank(x[, vars[i]])
}
} else {
if(varsign == "-") {
calllist[[i]] <- -x[, vars[i]]
} else {
calllist[[i]] <- x[,vars[i]]
}
}
}
return(x[do.call("order", calllist), ])
}

```