Plot geom_area with no filling and colouring lines by variable/ or geom_line without variables overlapping

Question

From what I can see, geom_area and geom_line plot variables differently so the area are on top of each other (they have different y-axis start) whereas geom_line they cross and overlap continuously. Do you know why is this?

I would like one of the following:

1. Using geom_area could I have no colour-filling for densities, and colour the lines selected variables based on “Case”?
2. Or could I use geom_line like I have done but avoiding the crossing and overlapping of variables?

Thanks

dataA <- tibble::tibble(
          value = c(10,20,30,30,20,10,5,8,10,8,7,2,9,25,28,29,15,6),
        Sample = rep(c(1:6),3),
        Variable = rep(c(rep("C1",6),rep("C2",6),rep("C3",6))),
        Case = rep(c(rep("o",6), rep("a",6),rep("o",6))))
    #This is the geom_area graph
        p1 <- ggplot(dataA, aes(x=Sample, y=value, fill=Variable)) +
        geom_area(colour="black", size=.2, alpha=.8) +
          theme_bw()
    #This is the geom_line
        p2 <- ggplot(dataA, aes(x=Sample, y=value, color=Case, group = interaction(Variable,Case))) + 
          geom_line(colour="black") +
          geom_line(data=subset(dataA, Case == "o"), colour="green4", size=1.5)

Answer 1

Use color instead fill in geom_area

library(ggplot2)
dataA <- tibble::tibble(
  value = c(10,20,30,30,20,10,5,8,10,8,7,2,9,25,28,29,15,6),
  Sample = rep(c(1:6),3),
  Variable = rep(c(rep("C1",6),rep("C2",6),rep("C3",6))),
  Case = rep(c(rep("o",6), rep("a",6),rep("o",6))))

ggplot(dataA, aes(x=Sample, y=value, group = interaction(Variable,Case))) +
  geom_area(aes(colour=Case), size=.2, alpha=.8, fill = NA) +
  theme_bw() +
  scale_color_manual(values = c("o" = "green4", "a" = "red"))

^{Created on 2020-04-20 by the reprex package (v0.3.0)}

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