r - Force ggplot2 to apply a separate legend for each geom

Question

In the chart below, the triangles mapped using geom_point are both in the same legend. Essentially, I would like each geom_ to have their own separate legend instead. How would I go about doing so?

Here's my code for reproducibility:

mydf <- data.frame(year = c(rep(2000, 3), rep(2002, 3), rep(2004, 3), rep(2006, 3), rep(2008, 3), rep(2010, 3), rep(2012, 3), rep(2014, 3), rep(2016, 3)),
                 answer = rep(c("A great deal", "Hardly any", "Only some"), 9),
                 result = c(0.3015940, 0.1399303, 0.5584757, 0.2269548, 0.1792754, 0.5937698, 0.2955301, 0.1309859, 0.5734840, 0.3008197, 0.1344499,
                            0.5647303, 0.1919454, 0.2026290, 0.6054256, 0.1059793, 0.4190533, 0.4749674, 0.1190636, 0.3631279, 0.5178085, 0.1518314,
                            0.3181203, 0.5300483, 0.1424715, 0.3094615, 0.5480669))
mydf$year <- factor(mydf$year)
mydf$answer <- factor(mydf$answer)
triangle_up <- data.frame(year = c(2004, 2008, 2010),
                        direction = c("A great deal", "Hardly any", "Hardly any"),
                        result = c(0.2955301, 0.2026290, 0.4190533))
triangle_up$year <- factor(triangle_up$year)
triangle_up$direction <- factor(triangle_up$direction)
triangle_down <- data.frame(year = c(2002, 2008, 2010, 2010, 2012),
                            direction = c(rep("A great deal", 3), "Only some", "Hardly any"),
                            result = c(0.2269548, 0.1919454, 0.1059793, 0.4749674, 0.3631279))
triangle_down$year <- factor(triangle_down$year)
triangle_down$direction <- factor(triangle_down$direction)

ggplot(mydf, aes(x = year, y = result)) + geom_line(aes(colour = answer, group = answer)) +
geom_point(data = triangle_up, aes(x = year, y = result, group = direction, fill = direction), shape = 24, size = 3) +
geom_point(data = triangle_down, aes(x = year, y = result, group = direction, fill = direction), shape = 25, size = 3)

Answer 1

The issue here is the use of multiple data frames to store values. It would be better to add a column to the mydf data frame to store the direction variable. Confusingly, you have used answer as the variable name in mydf, but direction to store the same values in the other data frames.

So here is the new mydf with values "up", "down" or NA in the direction column:

mydf <- structure(structure(list(year = c(2000, 2000, 2000, 2002, 2002, 2002, 2004, 
2004, 2004, 2006, 2006, 2006, 2008, 2008, 2008, 2010, 2010, 2010, 
2012, 2012, 2012, 2014, 2014, 2014, 2016, 2016, 2016), answer = structure(c(1L, 
2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 
3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L), .Label = c("A great deal", 
"Hardly any", "Only some"), class = "factor"), result = c(0.301594, 
0.1399303, 0.5584757, 0.2269548, 0.1792754, 0.5937698, 0.2955301, 
0.1309859, 0.573484, 0.3008197, 0.1344499, 0.5647303, 0.1919454, 
0.202629, 0.6054256, 0.1059793, 0.4190533, 0.4749674, 0.1190636, 
0.3631279, 0.5178085, 0.1518314, 0.3181203, 0.5300483, 0.1424715, 
0.3094615, 0.5480669), direction = c(NA, NA, NA, "down", NA, 
NA, "up", NA, NA, NA, NA, NA, "down", "up", NA, "down", "up", 
"down", NA, "down", NA, NA, NA, NA, NA, NA, NA)), .Names = c("year", 
"answer", "result", "direction"), row.names = c(NA, -27L), class = 
"data.frame"))

Now you can plot with separate legends for direction and answer. Shapes are specified manually using scale_shape_manual, using breaks to omit the NA values. For line colour, we use scale_color_manual and override the legend mapping so as only lines, not shapes, are shown.

ggplot(mydf, aes(year, result)) + 
  geom_line(aes(group = answer, color = answer)) + 
  geom_point(aes(shape = direction, fill = answer), size = 3) + 
  scale_shape_manual(values = c(25, 24), breaks = c("down", "up")) + 
  scale_color_manual(values = c("red", "green", "blue"),
                     guide = guide_legend(override.aes = list(shape = rep(NA, 3)))) +
  theme_light()