How to animate one line at a time using gganimate?

Question

I attempting to animate one line at a time using gganimate, where one line animates to completion before the next one starts.

Here is my current code:

library(gganimate)
library(reshape2)
library(ggplot2)



df <- data.frame(Index = c(1:10), a= 2*(1:10), b = 3*(1:10))

df <-  melt(df, id.vars = "Index")

ggplot(df, aes(x=Index, y = value, group = variable)) + 
  geom_line()+
  transition_reveal(Index)

This gives me the graph below, where both lines are animated simultaneously.

Answer 1

ggplot(transform(df, ind = 1:nrow(df)),
       aes(x=Index, y = value, group = variable)) + 
  geom_line()+
  transition_reveal(ind)