Combined line & bar geoms: How to generate proper legend?

Question

The legend for d2 looks fine; for d1, I would like to show just the hoizontal line against a white/transparent backgounnd.

df = dat         


        

Answer 1

# Bar graph: Notice the placement of fill argument in aes()  
  geom_bar(aes(y=prop.P*100, fill="Seropositive"), stat = "identity",
           position = "dodge", width = 0.5)+

# This line defines the legend for the bar
  scale_fill_manual(name="", values = c("Seropositive"="steelblue3"))+

# Adding errorbar
  geom_errorbar(aes(ymin = ciLow*100, ymax = ciHigh*100), width = 0.2,
                position = position_dodge(width=0.8))+

# Adding the line to the graph. Used the color argument within aes() to define custom colour
  geom_line(aes(y=mmr1_cov*100, group=1, color="MMR1 Coverage"), size=1)+

# Adding points represent the plotted data
  geom_point(aes(x=age, y=mmr1_cov*100), color="red", size=2)+

# Here adding the legend for the line graph and define the colour
  scale_color_manual(name="", values=c("MMR1 Coverage"="red"))+

# Label the axis
  labs(x="Age (Months)", y="Percentage")+

# Place the legend bottom of the graph
  theme(legend.position = "bottom")

Section of the graph displaying the results