Color plot depending on value but for multiple lines

Question

I need to create a plot from a data frame that contains data from multiple files. Some of the files are labelled as reference and some as user. I want to have smooth lines for each file, but the coloring should be done by label. Here is some test data for testing:

test <- data.frame(
  y = c(1, 2, 2, 3, 3, 4, 4, 5),
  x = rep(c(1, 2), 4),
  label = c("ref", "ref", "ref", "ref", "user", "user", "user", "user"),
  file = as.character(c(1, 1, 2, 2, 3, 3, 4, 4))
)

My current make-shift solution is to use shape=file:

ggplot(test, aes(x=x, y=y, color=label, shape=file)) +
  geom_point(size=3) + 
  geom_line() +  
  guides(shape=FALSE)

But I wonder whether there is a solution that does not rely on the shape, because I ideally want them to be the same. I already looked at the following questions, but they were all not helpful for my case:

• Assign color to lines ggplot2
• How do I have multiple lines of the same color with GG Plot
• Changing line colors with ggplot()

Answer 1

geom_line uses the group aesthetic to decide which points should be linked. So you can use:

ggplot(test, aes(x=x, y=y, color=label, group=file)) +
  geom_point(size=3) + 
  geom_line()

Your previous solution using shape worked because if group is absent ggplot uses the combinations of other discrete factors already specified (shape, fill, colour etc) as grouping factors.