Create a partial dashed line in ggplot2

Question

I\'m creating a plot in R and need to create a line where some of the values are projections. The projections are represented as a dashed line. Here\'s the code:

Answer 1

The ggplot philosopy is simple. Each element of a plot needs to be on a different layer. Thus to get two line segments in different line types, you need two geom_segment statements.

I illustrate the same principle with geom_bar in different colours for your different periods.

ggplot(df[df$date<=2011, ], aes(date, value, width=0.64)) + 
    geom_bar(stat = "identity", fill="#336699", colour="black") +
    geom_bar(data=df[df$date>2011, ], aes(date, value),  
        stat = "identity", fill="#336699", colour="black", alpha=0.5) +
    ylim(c(0,1400)) + opts(title="U.S. Smartphone Users") +
    opts(
        axis.text.y=theme_text(family="sans", face="bold"), 
        axis.text.x=theme_text(family="sans", face="bold"), 
        plot.title = theme_text(size=14, face="bold"), 
        axis.title.x=theme_text(family="sans"), 
        axis.title.y=theme_text(family="sans", angle=90)
    ) +
    xlab("Year") + ylab("Users (in millions)") +        
    geom_segment(aes(x=2007.6, xend=2011, y=550, yend=1050), linetype=1) + 
    geom_segment(aes(x=2011, xend=2013, y=1050, yend=1350), 
        arrow=arrow(length=unit(0.4,"cm")), linetype=2)