Two geom_points add a legend

Question

I plot a 2 geom_point graph with the following code:

source(\"http://www.openintro.org/stat/data/arbuthnot.R\")
library(ggplot2)
ggplot() +
  geom_point(aes(         


        

Answer 1

Here is a way of doing this without using reshape::melt. reshape::melt works, but you can get into a bind if you want to add other things to the graph, such as line segments. The code below uses the original organization of data. The key to modifying the legend is to make sure the arguments to scale_color_manual(...) and scale_shape_manual(...) are identical otherwise you will get two legends.

source("http://www.openintro.org/stat/data/arbuthnot.R")
library(ggplot2)
library(reshape2)



ptheme <- theme (
  axis.text            = element_text(size = 9),              # tick labels
  axis.title           = element_text(size = 9),              # axis labels
  axis.ticks           = element_line(colour = "grey70", size = 0.25),
  panel.background     = element_rect(fill = "white", colour = NA),
  panel.border         = element_rect(fill = NA, colour = "grey70", size = 0.25),
  panel.grid.major     = element_line(colour = "grey85", size = 0.25),
  panel.grid.minor     = element_line(colour = "grey93", size = 0.125),
  panel.margin         = unit(0 , "lines"),
  legend.justification = c(1, 0), 
  legend.position      = c(1, 0.1),
  legend.text          = element_text(size = 8),
  plot.margin          = unit(c(0.1, 0.1, 0.1, 0.01), "npc")   # c(bottom, left, top, right), values can be negative
)

cols    <- c( "c1" = "#ff00ff", "c2" = "#3399ff" )
shapes  <- c("s1" = 16, "s2" = 17)

p1 <- ggplot(data = arbuthnot, aes(x = year))
p1 <- p1 + geom_point(aes( y = boys,  color = "c1", shape = "s1"))
p1 <- p1 + geom_point(aes( y = girls, color = "c2", shape = "s2")) 
p1 <- p1 + labs( x = "Year", y = "Rate" )
p1 <- p1 + scale_color_manual(name = "Sex", 
                                breaks = c("c1", "c2"), 
                                values = cols,
                                labels = c("boys", "girls"))
p1 <- p1 + scale_shape_manual(name = "Sex", 
                              breaks = c("s1", "s2"),
                              values = shapes,
                              labels = c("boys", "girls"))
p1 <- p1 +  ptheme

print(p1)

output results