Stacked area chart in ggivs

stacked_area_chart.R

library(dplyr)
library(ggivs)

chart_data <- structure(list(CalYr = c(1990L, 1990L, 1990L, 1990L, 1990L, 1990L, 
1990L, 2000L, 2000L, 2000L, 2000L, 2000L, 2000L, 2000L, 2010L, 
2010L, 2010L, 2010L, 2010L, 2010L, 2010L, 2020L, 2020L, 2020L, 
2020L, 2020L, 2020L, 2020L), Speed = c(0, 10, 20, 30, 40, 50, 
60, 0, 10, 20, 30, 40, 50, 60, 0, 10, 20, 30, 40, 50, 60, 0, 
10, 20, 30, 40, 50, 60), VMT = c(323694, 940682, 25396442, 43050277, 
71101181, 16987641, 105467584, 222397, 859767, 57905435, 61835130, 
52478438, 13402243, 133584545, 591510, 2003120, 30768516, 80895398, 
80467412, 18261031, 129277323, 618255, 2114937, 32854406, 87450202, 
87820416, 19972164, 140161697)), class = "data.frame", row.names = c(NA, 
-28L), .Names = c("CalYr", "Speed", "VMT"))

# Stacked area chart
chart <- chart_data %>%
  arrange(CalYr, Speed) %>%
  mutate(to = cumsum(VMT), from = c(0, to[-n()])) %>%
  ggvis(x = ~CalYr, fill = ~Speed) %>%
  group_by(Speed) %>%
  layer_ribbons(y = ~from, y2 = ~to, fill = ~Speed) %>%
  add_axis("y", title = "VMT", format = "s") %>%
  add_axis("x", title = "Year", format = "d") 

# Works OK
chart %>%
  add_legend("fill", title = "MPH")

# Per example in `help("add_legend", package = "ggvis")`
# (but does not work)
chart %>%
  add_legend("fill", 
             title = "MPH",
             properties = legend_props(
               legend = list(x = scaled_value("x_rel", 0.1),
                             y = scaled_value("y_rel", 0.9))))