Would `scale_linewidth_discrete()` be developed to set values manually like other `scale_size_manual()`

[ZhangSR-kolar]

Hi~

I'd like to ask, would the scale_linewidth() be developed to scale_linewidth_manual(), so that I can set the specific value to different levels when I use a factor variable to constrain linewidth, just as scale_size_manual()?

Thanks!

[MatthewHeun]

I've been wondering this, too. Maybe to put it another way,

data.frame(x = 1:10, y = 11:20, which = c(rep("a", 5), rep("b", 5))) %>% 
ggplot2::ggplot() + 
ggplot2::geom_line(mapping = ggplot2::aes(x = x, y = y, 
                                          colour = which, 
                                          size = which)) + 
ggplot2::scale_size_manual(values = c(a = 0.5, b = 5))

was a very convenient way to set size (linewidth) manually (and programmatically). Maybe I missed it, but I don't see an equivalent way to set linewidth manually. (If there is a way, please let us know!)

ggplot2::scale_linewidth_manual() would be very convenient.

[clauswilke]

library(tidyverse)

data.frame(x = 1:10, y = 11:20, which = c(rep("a", 5), rep("b", 5))) %>% 
  ggplot() + 
  geom_line(aes(x, y, colour = which, linewidth = which)) + 
  scale_discrete_manual(aesthetic = "linewidth", values = c(a = 0.5, b = 5))

^{Created on 2022-11-20 by the reprex package (v2.0.1)}

Note that I'm generally in favor of having manual scales for all aesthetics. When I wanted to add some a few years ago it was vetoed and the accepted solution was scale_discrete_manual().

[MatthewHeun]

```r
library(tidyverse)

data.frame(x = 1:10, y = 11:20, which = c(rep("a", 5), rep("b", 5))) %>% 
  ggplot() + 
  geom_line(aes(x, y, colour = which, linewidth = which)) + 
  scale_discrete_manual(aesthetic = "linewidth", values = c(a = 0.5, b = 5))

Created on 2022-11-20 by the reprex package (v2.0.1)
Note that I'm generally in favor of having manual scales for all aesthetics. When I wanted to add some a few years ago it was vetoed and the accepted solution was scale_discrete_manual().

This worked. I was unaware of scale_discrete_manual(). Thanks!

[teunbrand]

Note that I'm generally in favor of having manual scales for all aesthetics.

I agree that that would make sense, but I can't find the counterarguments. I've seen a few times on SO that people were expecting scale_linewidth_manual() to exists.

[teunbrand]

In addition, scale_linewidth_identity() also doesn't exist.

[clauswilke]

@teunbrand This is the relevant discussion:
#2555 (comment)

I think it was mostly a "let's defer this decision" rather than "let's not do this". It's probably time to revisit this.

[thomasp85]

Both scale_linewidth_manual() and scale_linewidth_identity() has been omitted in error and should be added

[MatthewHeun]

Both scale_linewidth_manual() and scale_linewidth_identity() has been omitted in error and should be added

Thanks! That will be a big help to everyone.