ggplot group by one categorical variable and color by a second one

ggplot2, r

Solution

The problem is that the `group` aesthetic overrides the standard grouping protocols - it isn't included in the interaction of all discrete variables in the plot described in `?group`.

So, to get your plot to work without faceting you would need to manually specify the interaction

ggplot(dat) + geom_line(aes(x, value, group = interaction(rep,variable), color = variable), alpha = 0.3)

To override the alpha value in the aesthetic, use `guide_legend(override.aes = ...))`. This information can be found following the links in `?guides` and specifically `?guide_legend`

eg

ggplot(dat) + geom_line(aes(x, value, group = interaction(rep,variable), color = variable), 
                           alpha = 0.3) + 
  scale_colour_discrete(guide = guide_legend(override.aes = list(alpha = 1)))

Problem

Basically I'd like to create the first plot shown below in R using ggplot, but with both objects on the same graph (no facet wrapping). Consider a minimal example that mimics my data structure: ``` library(reshape2) library(ggplot2) x <- seq(1, 5, length = 100) y <- replicate(10, sin(2 * pi * x) + rnorm(100, 0, 0.3), "list") z <- replicate(10, sin(2 * pi * x) + rnorm(100, 5, 0.3), "list") y <- melt(y) z <- melt(z) df <- data.frame(x = y$Var1, rep = y$Var2, y = y$value, z = z$value) dat <- melt(df, id = c("x", "rep")) ``` I can plot it with ``` ggplot(dat) + geom_line(aes(x, value, group = rep, color = variable), alpha = 0.3) + facet_wrap(~variable) ``` And get (source: carlboettiger.info) But if I try dropping the facet wrapping, I thought it should group by color and variable, but instead the data are not broken out correctly, resulting in nonsense: (source: carlboettiger.info)

Original source