help_secondary is not working properly with geom_col

[bappa10085]

I am trying to use help_secondary with geom_col like

library(tidyverse)
library(ggh4x)
library(scales) 

# Run the secondary axis helper
sec <- help_secondary(df, primary = c(Tmax, Tmin, RH), 
                      secondary = Rainfall)

ggplot(df, aes(x = Date)) +
  geom_col(aes(y = sec$proj(Rainfall)), colour = "blue") +
  geom_line(aes(y = Tmax), colour = "red") +
  geom_line(aes(y = Tmin), colour = "green") +
  geom_line(aes(y = RH), colour = "black") +
  scale_y_continuous(sec.axis = sec) +
  ylab("Max and Min temperature, RH")

As you can see from the plot, the secondary y axis starts from -500. The 0 rainfall value is shown as -500 which ideally should be left out in the barplot. Another thing, how can I have the legend?

df = structure(list(Date = structure(c(18628, 18659, 18687, 18718, 
18748, 18779, 18809, 18840, 18871, 18901, 18932, 18962, 18993, 
19024, 19052, 19083, 19113, 19144, 19174, 19205, 19236, 19266, 
19297, 19327, 19358, 19389, 19417, 19448, 19478, 19509, 19539
), class = "Date"), Tmax = c(34.3774193548387, 34.8428571428571, 
35.7387096774194, 35.44, 34.1161290322581, 30.9333333333333, 
29.2193548387097, 29.9225806451613, 29.78, 32.4096774193548, 
32.97, 32.4129032258065, 32.2225806451613, 33.9428571428571, 
35.6, 35.2133333333333, 33.658064516129, 31.0566666666667, 29.4516129032258, 
29.6548387096774, 30.2066666666667, 32.4870967741935, 34.2566666666667, 
34.558064516129, 33.8161290322581, 36.3821428571429, 35.9483870967742, 
35.2266666666667, 35.9709677419355, 33.04, 28.6322580645161), 
    Tmin = c(21.5483870967742, 20.4714285714286, 24.1483870967742, 
    24.41, 25.2354838709677, 23.3966666666667, 23.2129032258064, 
    23.7935483870968, 24.6633333333333, 24.0225806451613, 23.3466666666667, 
    20.8516129032258, 19.3806451612903, 19.5, 23.558064516129, 
    24.9533333333333, 25.8741935483871, 23.92, 23.3709677419355, 
    22.8677419354839, 22.5433333333333, 21.7161290322581, 21.2133333333333, 
    21.0258064516129, 19.3612903225807, 20.6142857142857, 21.641935483871, 
    24.5343333333333, 26.0903225806452, 25.4443333333333, 23.7645161290323
    ), RH = c(62.1129032258064, 57.5892857142858, 70.4193548387097, 
    68.25, 74.8387096774194, 85.3333333333333, 88.5161290322581, 
    85.8870967741936, 86.4333333333334, 79.1129032258064, 74.6, 
    69.1935483870968, 62.6290322580645, 65.5892857142858, 66.3548387096774, 
    70.7166666666667, 75.7741935483871, 85.6833333333334, 88.3387096774194, 
    86.8064516129033, 84.1166666666667, 74.3870967741936, 64.4, 
    63.7903225806452, 60.1290322580645, 58.7321428571429, 58.4677419354839, 
    69.3, 65.9193548387097, 79.45, 91.6451612903226), Rainfall = c(9.1, 
    2, 0, 27, 422.6, 903.9, 1345.9, 343.9, 481, 239.9, 166.4, 
    105.9, 0, 0, 0.3, 51.2, 99.6, 700.6, 1098.3, 347.6, 276.8, 
    71.3, 0, 2.2, 0, 0, 0, 0, 0, 597, 1763.4)), row.names = c(NA, 
31L), class = "data.frame")

[bappa10085]

Taking help from this answer, I have solved the issue like

sec <- help_secondary(df, primary = c(Tmax, Tmin, RH),
                      secondary = Rainfall, method = "max")

ggplot(df, aes(x = Date)) +
  geom_col(aes(y = sec$proj(Rainfall), fill = "Rain")) +
  geom_line(aes(y = Tmax, color = "Tmax")) +
  geom_line(aes(y = Tmin, color = "Tmin")) +
  geom_line(aes(y = RH, color = "RH")) +
  scale_color_manual(values = c(Tmin = "green", Tmax = "red",
      RH = "black", Rain = "blue"), aesthetics = c("fill", "color")) +
  scale_y_continuous(sec.axis = sec) +
  labs(y = "Max and Min temperature, RH", color = NULL, fill = NULL) +
  guides(color = guide_legend(
    override.aes = list(fill = c("blue", rep("transparent", 3)))
  ))

In help_secondary, the default methods of projecting the secondary axis data is range. But in documentation, it has not been mentioned. It would be better to mention it.

[teunbrand]

This is because the secondary helper doesn't know about geom_col(), so it won't know that the data range should include 0 even though every value is more than 0. I'd propose that a fix is to just include 0 as primary data, e.g.:

sec <- help_secondary(df, primary = c(Tmax, Tmin, RH, 0), 
                      secondary = Rainfall)