How do I seperate two overlapping legends for a dual axis ggplot, one legend representing variables-CodePudding

I have the following dataframe as a reprex:

weather <- data.frame(time= c("12:19","12:15","13:20","13:22","16:19"), sensor_rh = c("A","B","C","A","A"), sensor_t = c("A","B","C","C","A"), t = c(30.4,29.4,29.4,30.3,28.9), rh = c(66.8,67.1,67.6,67.1,68.0))

I want the plot to show me two different shapes, distinguishing the rh and t variables, and three colors, distinguishing the sensors for rh and t.

I am managing to plot the points as desired in a scatterplot with a primary axis for the variable relative humidity (rh) and a secondary axis for the variable temperature (temp). However, as an example, the following code does not give me two seperate legends; one for the variables and one for the sensors.

scale <- 2
ggplot(weather, aes(x = time))  
  geom_point(aes(y = rh, color = sensor_rh), shape = 1)  
  geom_point(aes(y = t*scale, color = sensor_t), shape = 3)  
  scale_color_manual(name = "sensor", values = c("A" = "red", "B" = "blue", "C" = "green"), guide = guide_legend(title = "Sensor", title.position = "top", title.hjust = 0.5 ))  
  scale_shape_manual(name = "variable", values = c("rh" =1, "t" = 3), guide = guide_legend(title = "variable", title.position = "top", title.hjust = 0.5))  
  scale_y_continuous(name = "rh(%)", sec.axis = sec_axis(~./scale, name = "t(°C)"))   
  labs(x= "time")

scatterplot with dual axis only one (overlapping)legend

Can someone help me figure out how to plot the desired graph? I feel I have played around with the code in so many ways, with questions that seem almost duplicate to mine, but mostly I either do not get correctly plotted scatter points or I dont get a seperate legend.

It seems that the shapes are overlapping for the two variables.

I know there is controversy in the use of dual axis, but please lets not get into that discussion here.

Thank you in advance!

CodePudding user response：

Instead of setting the shape as an argument map on the shape aesthetic, i.e. inside aes(). As you already included scale_shape_manual you could use shape="rh" and shape="t" in your geom_point layers:

library(ggplot2)

scale <- 2
ggplot(weather, aes(x = time))  
  geom_point(aes(y = rh, color = sensor_rh, shape = "rh"))  
  geom_point(aes(y = t * scale, color = sensor_t, shape = "t"))  
  scale_color_manual(
    name = "sensor", values = c("A" = "red", "B" = "blue", "C" = "green"),
    guide = guide_legend(title = "Sensor", title.position = "top", title.hjust = 0.5)
  )  
  scale_shape_manual(
    name = "variable", values = c("rh" = 1, "t" = 3),
    guide = guide_legend(title = "variable", title.position = "top", title.hjust = 0.5)
  )  
  scale_y_continuous(name = "rh(%)", sec.axis = sec_axis(~ . / scale, name = "t(°C)"))  
  labs(x = "time")