changing individual densities to match legend in ggplot2

Question

I'm working on overlaying several density plots to create a figure in ggplot2. Say I have data points for each December over a series of years (in this case 2004-2012) and I want to plot a density function for each December month + year and overlay them. I would like to highlight one density line for a specific month by making it dashed where all the others are solid. I have a reproducible example below:

#Create vector of data for December 
set.seed(12345)
dec_emas = as.matrix(rnorm(496, 122, 250))

#create indicators for Dec04 ... Dec11, then attach to data frame w/ estimates
declab = c('Dec04', 'Dec05', 'Dec06', 'Dec07', 'Dec08', 'Dec09', 'Dec10', 'Dec11')
declabs = rep(declab, 62)

rownames(dec_emas) = declabs
colnames(dec_emas) = 'EMA'

#add in factor ID for the 8 levels 
dec04 = as.numeric(rownames(dec_emas) == 'Dec04')
dec05 = as.numeric(rownames(dec_emas) == 'Dec05')
dec06 = as.numeric(rownames(dec_emas) == 'Dec06')
dec07 = as.numeric(rownames(dec_emas) == 'Dec07')
dec08 = as.numeric(rownames(dec_emas) == 'Dec08')
dec09 = as.numeric(rownames(dec_emas) == 'Dec09')
dec10 = as.numeric(rownames(dec_emas) == 'Dec10')
dec11 = as.numeric(rownames(dec_emas) == 'Dec11')

dec_ema = as.numeric(dec_emas)
dec_ema_df = data.frame(dec_ema, dec04,dec05,dec06,dec07,dec08,dec09,dec10,dec11)

dec_ema_df$new[dec_ema_df$dec04==1]<-4
dec_ema_df$new[dec_ema_df$dec05==1]<-5
dec_ema_df$new[dec_ema_df$dec06==1]<-6
dec_ema_df$new[dec_ema_df$dec07==1]<-7
dec_ema_df$new[dec_ema_df$dec08==1]<-8
dec_ema_df$new[dec_ema_df$dec09==1]<-9
dec_ema_df$new[dec_ema_df$dec10==1]<-10
dec_ema_df$new[dec_ema_df$dec11==1]<-11


#using GGPLOT2... 
library(ggplot2)
library('RColorBrewer')


#use different colours for each december 
cbbPalette <- brewer.pal(8, "Accent")

#Plot overlaid densities and highlight December 08 with a dashed line. 
dec.dens1 = ggplot(dec_ema_df, aes(x=dec_ema, group = new)) + 
  geom_density(aes(colour=factor(new), linetype = factor(new==8)), size = 1, alpha = .60, kernel='epanechnikov') + 
  xlab(NULL) + ylab(NULL) + 
  scale_linetype_manual(values = c('solid', 'dashed'),  guide = FALSE) +
  scale_colour_manual(values = cbbPalette,
                      labels= c('Dec `04','Dec `05','Dec `06','Dec `07','Dec `08','Dec `09','Dec `10','Dec `11'),
                      name= '')             


print(dec.dens1)

Currently, I'm able to produce this. Unfortunately the legend on the right shows a solid blue line for Dec '08 instead of a dashed line. How can I make the legend correspond to the dashed density line for only Dec '08 (e.g. all other legend keys are solid lines)? I have tried using legend.key but this only works for the outline and background not the actual object in the legend.

Answer 1

If you map your factor new to both colour and linetype, and specify the same labels for both scales, then ggplot will happily combine the colour and linetype legends automatically:

dec.dens1 = ggplot(dec_ema_df, aes(x=dec_ema, group=new)) + 
            geom_density(aes(colour=factor(new), linetype=factor(new)), 
                         size=1, alpha=.60, kernel='epanechnikov') + 
            xlab(NULL) +
            ylab(NULL) + 
            scale_linetype_manual(values=c('solid', 'solid','solid','solid',
                                           'dashed','solid','solid','solid'),
                            labels=c('Dec `04','Dec `05','Dec `06','Dec `07',
                                     'Dec `08','Dec `09','Dec `10','Dec `11')) +
            scale_colour_manual(values = cbbPalette,
                            labels=c('Dec `04','Dec `05','Dec `06','Dec `07',
                                     'Dec `08','Dec `09','Dec `10','Dec `11'))