ggplot2: Change Alpha of scale_color_viridis_c but not legend

Question

I'd like to add an alpha to my ggplot but not impact the alpha of the legend. The current solution is to add the override of : guides(color = guide_legend(override.aes = list(alpha = 1))) . This works to set alpha=1 but changes the legend scale to discrete points instead of a scale.

How can I change the alpha of my color scale while retaining full visibility and the actual scale in the legend?

Example Code:

library(ggplot2)

###Generate Mock Data ###
df<- data_frame(y=seq(1:100), x=seq(1:100), z=seq(1:100))

###Plot without Alpha ###
df %>% ggplot(aes(x=x, y=y, color=z)) +
  geom_point()+
  scale_color_viridis_c()

###Plot with Alpha showing alpha on legend with continuous scale ###
df %>% ggplot(aes(x=x, y=y, color=z)) +
      geom_point()+
      scale_color_viridis_c(alpha=0.01)

###Plot with Alpha showing alpha=1 on legend but scale changed to discrete###

df %>% ggplot(aes(x=x, y=y, color=z)) +
  geom_point()+
  scale_color_viridis_c(alpha=0.5)+
  guides(color = guide_legend(override.aes = list(alpha = 1)))

Answer 1

You can simply add your alpha to the geom_point() rather than the colour scale. Below is a reproducable example highlighting the difference between your current approach and the correct way to acchieve what you have asked, ie, 'How can I change the alpha of my color scale while retaining full visibility and the actual scale in the legend?'

library(ggplot2)
library(vctrs)

###Generate Mock Data ###
df<- data_frame(y=seq(1:100), x=seq(1:100), z=seq(1:100))

###Plot with Alpha = 0 showing points and legend disappears###
ggplot(df,aes(x,y,color=z)) +
      geom_point()+
      scale_color_viridis_c(alpha=0.00)

###Plot with Alpha = 0.1 showing points and legend disappears###
ggplot(df,aes(x,y,color=z)) +
      geom_point()+
      scale_color_viridis_c(alpha=0.1)

###Plot with Alpha = 0 showing points disappear while legend remains visible###
ggplot(df,aes(x,y,color=z)) +
  geom_point(alpha=0.00)+
  scale_color_viridis_c()

###Plot with Alpha = 0 showing points disappear while legend remains visible###
ggplot(df,aes(x,y,color=z)) +
  geom_point(alpha=0.1)+
  scale_color_viridis_c()