Add the quantilies to each line, ggplot2 - r

Question

I am trying to shade the 0.025 and 0.975 quantiles on this graph that has three lines. I have tried geom_area, geom_ribbon, and I cannot highlight every quantile in every line.
Please note that "y" was ignored in this density graph.
example <-data.frame(source=c("Leaflitter","Leaflitter","Leaflitter","Leaflitter",
"Leaflitter","Leaflitter","Leaflitter","Leaflitter","Leaflitter","Leaflitter",
"Biofilm","Biofilm","Biofilm","Biofilm","Biofilm","Biofilm","Biofilm","Biofilm",
"Biofilm","Biofilm","Algae","Algae","Algae","Algae","Algae","Algae","Algae","Algae",
"Algae","Algae"), n=c(1,2,3,4,5,6,7,8,9,10,1,2,3,4,5,6,7,8,9,10,1,2,3,4,5,6,7,8,9,10),
density=c(0.554786934, 0.650578421, 0.039317168, 0.53537613,0.435081982,0.904056941,0.556284164,0.855319434,
0.399169622,0.570246304,0.076722032,0.257427999,0.172736928,0.447424473,0.520976948,0.011720494,0.311348655,
0.120698996,0.016336661,0.331741377, 0.368491034,0.09199358,0.787945904,0.017199397,0.04394107,
0.084222564,0.132367181,0.023981569,0.584493716,0.098012319))
example
One subgroup and quantiles
L <- filter(QPA_G_Feb17, source == "Leaflitter")
L <-as.data.frame(L)
Lq025 <- quantile(L$density, .025)
Lq975 <- quantile(L$density, .975)
ggplot(QPA_G_Feb17, aes(x=density, color=source)) +
labs(y="Density", x="Sorce contribution") +
geom_density(aes(linetype = source), size=1.2) +
scale_color_manual(values=c("#31a354", "#2c7fb8", "#d95f0e")) +
scale_linetype_manual(values = c("solid", "dotted", "longdash")) +
theme_classic()+
ylim(0, 5)+
theme(axis.text.y=element_text(angle=0, size=12, vjust=0.5, color="black")) +
theme(axis.text.x =element_text(angle=0, size=12, vjust=0.5, color="black")) +
theme(axis.title.x = element_text(color="black", size=14))+
theme(axis.title.y = element_text(color="black", size=14))
I would appreciate your help since I have looked in other forums, and there is information to highlight when there is only 1 line.

Answer 1

I think this data is a bit more representative of the data displayed in your plot:
set.seed(50)
QPA_G_Feb17 <- data.frame(density = c(rgamma(400, 2, 10),
rgamma(400, 2.25, 9),
rgamma(400, 5, 7)),
source = rep(c("Algae", "Biofilm", "Leaflitter"),
each = 400))
I find that when you are trying to do something complex or non-standard in ggplot, the best thing to do is calculate the data you wish to plot ahead of time. In this case, we can calculate the density curves and the cumulative densities, including their 0.025 and 0.975 quantiles, and putting them all in a data frame like this:
dens <- lapply(split(QPA_G_Feb17, QPA_G_Feb17$source),
function(x) density(x$density, from = 0, to = 1))
df <- do.call(rbind, mapply(function(x, y) {
data.frame(x = x$x, y = x$y, source = y)
}, dens, names(dens), SIMPLIFY = FALSE))
df <- df %>%
group_by(source) %>%
mutate(cdf = cumsum(y * mean(diff(x))),
lower = cdf < 0.025,
upper = cdf > 0.975)
Now it is easy to plot using geom_area:
ggplot(df, aes(x, y, color = source)) +
geom_area(data = df[df$lower,], aes(fill = source), alpha = 0.5,
position = "identity") +
geom_area(data = df[df$upper,], aes(fill = source), alpha = 0.5,
position = "identity") +
labs(y = "Density", x = "Source contribution") +
geom_line(aes(linetype = source), size = 1.2) +
scale_fill_manual(values = c("#31a354", "#2c7fb8", "#d95f0e")) +
scale_color_manual(values = c("#31a354", "#2c7fb8", "#d95f0e")) +
scale_linetype_manual(values = c("solid", "dotted", "longdash")) +
theme_classic() +
ylim(0, 5) +
xlim(0, 1) +
theme(axis.text.y = element_text(size = 12, vjust = 0.5),
axis.text.x = element_text(size = 12, vjust = 0.5),
axis.title.x = element_text(size = 14),
axis.title.y = element_text(size = 14))
Here, the 2.5% and 97.5% extremeties of each density curve are shaded below each line. The exception is in the "Leaflitter` line, which clearly extends out of the 0-1 range that has been plotted in your example.