Get names of a color based on alpha value-CodePudding

Let say I supply R with a color name '#023e8a'

Now I want to get 5 following color names with alpha values as c(0.8, 0.6, 0.5, 0.3, 0.2), which will be passed to ggplot as fill aesthetics.

Is there any function available in R or ggplot to achieve this? I know that in ggplot I could pass alpha values in any layer, but I want to get specific names of the color shades.

Any pointer will be very appreciated.

CodePudding user response：

One option to get the color "names" with alpha applied would be to use scales::alpha.

library(ggplot2)
library(scales)

dat <- data.frame(
  x = LETTERS[1:5],
  y = 1:5
)

ggplot(dat, aes(x, y, fill = x))  
  geom_col()  
  scale_fill_manual(values = scales::alpha('#023e8a', c(0.8, 0.6, 0.5, 0.3, 0.2)))

If instead of adding transparency you just want different shades of a color then perhaps colorspace::lighten is more appropriate:

ggplot(dat, aes(x, y, fill = x))  
  geom_col()  
  scale_fill_manual(values = colorspace::lighten('#023e8a', 1 - c(0.8, 0.6, 0.5, 0.3, 0.2)))

CodePudding user response：

You can use scales::alpha:

library(scales)
alpha("#023e8a", c(0.8, 0.6, 0.5, 0.3, 0.2))
#[1] "#023E8ACC" "#023E8A99" "#023E8A80" "#023E8A4C" "#023E8A33"

CodePudding user response：

The other answers are good and I would use them.

However, if you are trying to reduce package dependencies, you can create a function that appends the hex value of each scaled alpha value to the color code:

append_alpha  <- function(color, alpha) {
    alpha_scaled  <- round(alpha*255)
    alpha_hex  <- as.hexmode(alpha_scaled)
    color_with_alpha  <- paste0(color, alpha_hex)

    return(color_with_alpha)
}

alpha_values  <- c(0.8, 0.6, 0.5, 0.3, 0.2)
append_alpha("#023e8a", alpha_values)
# "#023e8acc" "#023e8a99" "#023e8a80" "#023e8a4c" "#023e8a33"

If you are reducing dependencies because you are building code that other people will use, you will want to add some error handling for blank strings, invalid colors etc.