Easy way to manipulate individual hcl axes?

[hadley]

Something like this maybe:

modify_hcl <- function(x, h, c, l) {
  hcl <- as.data.frame(farver::decode_colour(x, to = "hcl"))

  if (!missing(h)) {
    h <- eval(substitute(h), envir = hcl)
  } else {
    h <- hcl$h
  }
  if (!missing(c)) {
    c <- eval(substitute(c), envir = hcl)
  } else {
    c <- hcl$c
  }
  if (!missing(l)) {
    l <- eval(substitute(l), envir = hcl)
  } else {
    l <- hcl$l
  }
  
  farver::encode_colour(cbind(h, c, l), from = "hcl")
}

Idea is to make it easy to do (e.g.) modify_hcl(x, h = 25) or modify_hcl(x, h = h + 10)

[EmilHvitfeldt]

I was waiting for someone to suggest this, so now it is time :)

I like eval steps. Design-wise I think I'm going to split this function (and others) so we have modify_hue(), modify_chroma() etc etc. I would properly still keep modify_hcl() as shorthand, as I think it is important that the function names reflect what we are working with.

[hadley]

I think having individual functions would be a substantial decrease in usability.

[EmilHvitfeldt]

Could you expand on your reasoning?

Adding

• modify_hue()
• modify_chroma()
• modify_ luminance()
• modify_hcl()

vs

• modify_hcl()

Is it because it would add many more functions with redundancy?

[hadley]

Right, this is a lot of typing:

x %>% 
  modify_hue(50) %>%
  modify_chroma(10)

Compared to:

x %>% modify_hcl(h = 50, c = 10)

I think it's reasonable to assume that people know what h, c, and l stand for in a colour manipulation package.

Also note that these two operations don't necessarily produce the same colour:

x %>% 
  modify_hue(50) %>%
  modify_chroma(10)

x %>% 
  modify_chroma(10) %>%
  modify_hue(50)

Really you want to do all the modifications in one transformation to hcl space, rather than going back and forth to and from rgb multiple times.

[EmilHvitfeldt]

I happened! It took a while for me to get around to it

[hadley]

Thanks!