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colourvalues

What does it do?

It maps viridis colours (by default) to values, and quickly!

Note It does not perform a 1-to-1 mapping of a palette to values. It interpolates the colours from a given palette.

Why did you build it?

I’m aware there are other methods for mapping colours to values. And which do it quick too. But I can never remember them, and I find the interfaces a bit cumbersome. For example, scales::col_numeric(palette = viridisLite::viridis(5), domain = range(1:5))(1:5).

I wanted one function which will work on one argument.

I also want it available at the src (C/C++) level for linking to other packages.

Why do you spell colour with a ‘u’?

Because it’s correct, and R tells us to

For consistency, aim to use British (rather than American) spelling

But don’t worry, color_values(1:5) works as well

How do I install it?

From CRAN

install.packages("colourvalues")

Or install the development version from GitHub with:

How can I make use of it in my package?

Rcpp

All functions are written in Rcpp. I have exposed some of them in header files so you can “link to” them in your package.

For example, the LinkingTo section in DESCRIPTION will look something like

And in a c++ source file so you can #include a header and use the available functions

R

If you’re not using Rcpp, just Import this package like you would any other.

Do you have any examples?

Of course!

256 numbers mapped to a colour

bar_plot <- function(df) {
  barplot( height = df[["a"]], col = df[["col"]], border = NA, space = 0, yaxt = 'n')
}
df <- data.frame(a = 10, x = 1:256)
df$col <- colour_values(df$x, palette = "viridis")
bar_plot( df )

5000 numbers on a non-linear scale

df <- data.frame(a = 10, x = c((1:5000)**3))
df$col <- colour_values(df$x, palette = "viridis")
bar_plot( df )

1000 random numbers

df <- data.frame(a = 10, x = rnorm(n = 1000))
df$col <- colour_values(df$x, palette = "inferno")
bar_plot( df )

Eurgh!

That’s better!

Do I have to use the in-built palettes?

No, you can use your own specified as a matrix of red, green and blue columns in the range [0,255]

n <- 100
m <- grDevices::colorRamp(c("red", "green"))( (1:n)/n )
df <- data.frame(a = 10, x = 1:n)
df$col <- colour_values(df$x, palette = m)
bar_plot( df )

Do you support ‘alpha’ values

Yep. Either supply a single alpha value for all the colours

Or use a vector of values the same length as x

df <- data.frame(a = 10, x = 1:300, y = rep(c(1:50, 50:1), 3) )
df$col <- colour_values(df$x, alpha = df$y)
bar_plot( df )

Or include the alpha value as a 4th column in the palette matrix

n <- 100
m <- grDevices::colorRamp(c("red", "green"))( (1:n)/n )
## alpha values
m <- cbind(m, seq(0, 255, length.out = 100))
df <- data.frame(a = 10, x = 1:n)
df$col <- colour_values(df$x, palette = m)
bar_plot( df )

Some of my plotting functions don’t support alpha, can I exclude it?

Yep. Set include_alpha = FALSE

Can I get a summary of colours to use in a legend?

Yes, for numeric values use the n_summaries argument to specify the number of summary values you’d like

You can also specify the number of digits you’d like returned in the summary

You can also use format = FALSE if you don’t want the summary values formatted.

For categorical values use summary = TRUE to return a uniqe set of the values, and their associated colours