How to add a label for a vertical line with legend in ggplot2

Question

R 3.1.2/ggplot2_1.0.0/Windows7

How can one add 2 vertical lines with legends in a faceted graph without them changing the linetype? In the following example i can't get the legends to appear as I would imagine them to (two solid lines and a adecuate legend) from the code I'm writing. A reproducible example:

library(ggplot2)
library(plyr)
library(e1071)

set.seed(89)
pm <- data.frame(pm10=rnorm(400, 150, 50), estacion=gl(4,100, labels = c('sur', 'norte', 'este', 'oeste')))   # data
curtosis <- ddply(pm, .(estacion), function(val) sprintf("curtosis==%.2f", kurtosis(val$pm10)))
asimetria <- ddply(pm, .(estacion), function(val) sprintf("asimetría==%.2f", skewness(val$pm10)))

p1 <- ggplot(data=pm, aes(x=pm10, y=..density..)) +
  geom_histogram(bin=15, fill='#deebf7', colour='#bdbdbd')+
  geom_density(size=1, colour='#cccccc')+
  geom_vline(data=aggregate(pm[1], pm[2], quantile, .8), mapping=aes(xintercept=pm10, linetype='percentil .8'), size=1, colour='#dfc27d', show_guide = T)+
  geom_vline(data=aggregate(pm[1], pm[2], median), mapping=aes(xintercept=pm10, linetype='mediana'), size=1, colour='#80cdc1', show_guide = T)+
  geom_text(data=curtosis, aes(x=350, y=.010, label=V1), size=3, parse=T)+
  geom_text(data=asimetria, aes(x=350, y=.008, label=V1), size=3, parse=T)+
  guides(linetype=guide_legend(override.aes=list(colour = c("#dfc27d","#80cdc1"))))+
  xlim(0,500)+
  facet_wrap(~ estacion, ncol=2) 

print(p1)

I want the lines to be solid (color is ok) and the legend's title to say: "Medida de tendencia".

Answer 1

The main idea for rather compicated ggplots like yours is to separate the data preparation from actual plotting. Within the data preparation step you can organize your data according to the plotting concept you have in mind.

In your case this implies precomputing the statistic in question:

df_vline <- rbind(
  aggregate(pm[1], pm[2], quantile, .8), 
  aggregate(pm[1], pm[2], median)
)
df_vline$stat <- rep(c("percentil .8", "mediana"), each = nrow(df_vline) / 2)

and then the mapping scheme is quite straightforward, so you don't have to think about manual overriding of the legend.

ggplot(data=pm, aes(x=pm10, y=..density..)) +
  geom_histogram(bin=15, fill='#deebf7', colour='#bdbdbd')+
  geom_density(size=1, colour='#cccccc')+
  geom_vline(data=df_vline, mapping=aes(xintercept=pm10, colour = stat), 
             linetype = 1, size=1, show_guide = T)+
  geom_text(data=curtosis, aes(x=350, y=.010, label=V1), size=3, parse=T)+
  geom_text(data=asimetria, aes(x=350, y=.008, label=V1), size=3, parse=T)+
  scale_colour_manual(values = c("#dfc27d","#80cdc1"), name = "Medida de tendencia")+
  xlim(0,500)+
  facet_wrap(~ estacion, ncol=2) 

(Nice plot, by the way.)