How to change legend title position when I have multiple scales created with ggnewscale package?

Question

I created a plot which has 2 color scales and 2 linetype scales made with the ggnewscale package. I want the legend to appear at the bottom of the plot and the legend titles to appear above the labels. I did it halfway, because in my attempts, the first scales (from geom_vline()) don't appear the way I want. I even tried to indicate the desired position of this scale before declaring the next scales with new_scale() and new_scale_color().Does anyone know how I can fix this?

library(ggplot2)
library(ggnewscale)

mtcars$cyl <- factor(mtcars$cyl)

# Attempt 1

ggplot(data = mtcars,
       aes(x = wt,
           y = mpg)) +
  geom_vline(aes(xintercept = gear,
                 color = "Important line",
                 linetype = "Important line")) +
  scale_linetype_manual(name = "Important lines",
                        values = 1) +
  scale_color_manual(name = "Important lines",
                     values = "red") +
  new_scale("linetype") +
  new_scale_color() +
  geom_line(aes(linetype = cyl,
                color = cyl)) +
  theme(legend.position = "bottom") +
  guides(linetype = guide_legend(title.position = "top"),
         color = guide_legend(title.position = "top"))

# Attempt 2

ggplot(data = mtcars,
       aes(x = wt,
           y = mpg)) +
  geom_vline(aes(xintercept = gear,
                 color = "Important line",
                 linetype = "Important line")) +
  scale_linetype_manual(name = "Important lines",
                        values = 1) +
  scale_color_manual(name = "Important lines",
                     values = "red") +
  guides(linetype = guide_legend(title.position = "top",
                                 label.position = "bottom"), # Before new scales
         color = guide_legend(title.position = "top",
                              label.position = "bottom")) +
  new_scale("linetype") +
  new_scale_color() +
  geom_line(aes(linetype = cyl,
                color = cyl)) +
  theme(legend.position = "bottom") +
  guides(linetype = guide_legend(title.position = "top"),
         color = guide_legend(title.position = "top"))

Both attempts produce the same plot, which is not what I want.

Answer 1

Not sure wether there is another option but what worked for me when making use of ggnewscale is to style the guide via the guide argument of the scale. To make this work I added a ´scale_color_discrete`:

library(ggplot2)
library(ggnewscale)

mtcars$cyl <- factor(mtcars$cyl)

ggplot(data = mtcars,
       aes(x = wt,
           y = mpg)) +
  geom_vline(aes(xintercept = gear,
                 color = "Important line",
                 linetype = "Important line")) +
  scale_linetype_manual(name = "Important lines",
                        values = 1, guide = guide_legend(title.position = "top") ) +
  scale_color_manual(name = "Important lines",
                     values = "red", guide = guide_legend(title.position = "top")) +
  new_scale("linetype") +
  new_scale_color() +
  geom_line(aes(linetype = cyl,
                color = cyl)) +
  scale_color_discrete(guide = guide_legend(title.position = "top")) +
  theme(legend.position = "bottom")