Adjust Transparency (alpha) of stat_smooth lines, not just transparency of Confidence Interval
RGgplot2TransparencyAlphaR Problem Overview
Using ggplot2's stat_smooth(), I'm curious how one might adjust the transparency of the generated regression line. Using geom_points() or geom_line(), one normally sets a value for 'alpha', indicating the percent transparency. However, with stat_smooth(), alpha sets the transparency of the confidence interval (in my sample below, turned off - se=FALSE).
I cannot seem to find a way to make the regression line(s) a lower transparency than 1.
Your advice would be wonderful.
Sample Code
library(reshape2)
df <- data.frame(x = 1:300)
df$y1 <- 0.5*(1/df$x + 0.1*(df$x-1)/df$x + rnorm(300,0,0.015))
df$y2 <- 0.5*(1/df$x + 0.3*(df$x-1)/df$x + rnorm(300,0,0.015))
df$y3 <- 0.5*(1/df$x + 0.6*(df$x-1)/df$x + rnorm(300,0,0.015))
df <- melt(df, id = 1)
ggplot(df, aes(x=x, y=value, color=variable)) +
geom_point(size=2) +
stat_smooth(method = "lm", formula = y ~ 0 + I(1/x) + I((x-1)/x),
se = FALSE,
size = 1.5,
alpha = 0.5)
R Solutions
Solution 1 - R
To set alpha value just for the line you should replace stat_smooth()
with geom_line()
and then inside the geom_line()
use the same arguments as in stat_smooth()
and additionally add stat="smooth"
.
ggplot(df, aes(x=x, y=value, color=variable)) +
geom_point(size=2) +
geom_line(stat="smooth",method = "lm", formula = y ~ 0 + I(1/x) + I((x-1)/x),
size = 1.5,
linetype ="dashed",
alpha = 0.5)
Solution 2 - R
As an alternative that's slightly more intuitive -- perhaps created since this answer -- you can use stat_smooth (geom="line")
. The SE envelope disappears, though you can add it back with something like:
geom_smooth (alpha=0.3, size=0, span=0.5)
stat_smooth (geom="line", alpha=0.3, size=3, span=0.5) +
The first line creates the SE. with no (0-width) line, and the second line adds the line over top of it. The (current) documentation mentions that stat_smooth
is for non-standard geoms (e.g. "line").