Create a secondary y axis for lines graph with ggvis R

Question

This is what i have so far with the ggvis package in R.

    mtcars %>% ggvis(x = ~disp) %>% 
    layer_lines(y = ~wt, stroke := "red") %>%
    layer_lines(y = ~mpg) %>%
    add_axis("y", orient = "left", title = "Weight (lb/1000)") %>%
    add_axis("y", orient = "right", title= "Miles/(US) gallon") %>%
    add_axis("x", title = "Displacement (cu.in.)")

I cannot get the left Y axis to represent the wt scale data.

This outputs:

Answer 1

I assume you want the left y axis (i.e. wt) divided by 1000:

library(dplyr) #you need this library
mtcars  %>% mutate(wt_scaled=wt/1000)  %>% ggvis(x = ~disp) %>% #use mutate from dplyr to add scaled wt
  layer_lines(y = ~wt_scaled, stroke := "red") %>% #use new column
  add_axis("y", orient = "left", title = "Weight (lb/1000)" ,title_offset = 50) %>% #fix left axis label
  scale_numeric("y", domain = c(0, 0.006), nice = FALSE) %>% #align the ticks as good as possible
  add_axis("y", 'ympg' , orient = "right", title= "Miles/(US) gallon" , grid=F ) %>% #remove right y axis grid and name axis
  layer_lines( prop('y' , ~mpg,  scale='ympg') ) %>% #use scale to show layer_lines which axis it should use
  add_axis("x", title = "Displacement (cu.in.)"  )

and I think this is what you want:

EDIT:

If you just wanted to plot wt on the left y axis (it is not very clear) then do mutate(wt_scaled=wt/1) (or remove mutate) and change domain to domain = c(1.5, 5.5)