Use dropdown in R plotly to update both trace and axis title

plotly_r_update_trace_and_axis.R

## Makes plot of either mpg or hp versus wt using mtcars dataset
## Dropdown enables toggling between what variable to plot on y axis

library(plotly)
plot_ly(mtcars, x = ~wt) %>%
  add_markers(y = ~mpg, name = "mpg") %>%
  add_markers(y = ~hp, name = "hp", visible = FALSE) %>%
  layout(
    title = "Drop down menus - Update",
    xaxis = list(domain = c(0.1, 1)),
    yaxis = list(title = "mpg"),
    showlegend = FALSE,
    updatemenus = list(
      list(
        y = 0.7,
        buttons = list(
          list(method = "update",
               args = list(list(visible = list(TRUE, FALSE)),
                           list(yaxis = list(title = "mpg"))),
               label = "mpg"),

          list(method = "update",
               args = list(list(visible =  list(FALSE, TRUE)),
                           list(yaxis = list(title = "hp"))),
               label = "hp")))
    )
  )