gganimate: include additional variable other than states level variable or frame in title expression

Question

I'd like to insert another column value of my data into a gganimate animation title.

Example, here the states level variable is x and I'd like to add to title variable y:

df <- tibble(x = 1:10, y = c('a', 'a', 'b', 'd', 'c', letters[1:5]))
df

A tibble: 10 x 2
       x y    
   <int> <chr>
 1     1 a    
 2     2 a    
 3     3 b    
 4     4 d    
 5     5 c    
 6     6 a    
 7     7 b    
 8     8 c    
 9     9 d    
10    10 e 

This works as expected:

ggplot(df, aes(x, x)) +
  geom_point() +
  labs(title = '{closest_state}') +
  transition_states(x,
                    transition_length = 0.1,
                    state_length = 0.1)

This fails:

ggplot(df, aes(x, x)) +
  geom_point() +
  labs(title = '{closest_state}, another_var: {y}') +
  transition_states(x,
                    transition_length = 0.1,
                    state_length = 0.1)

Error in eval(parse(text = text, keep.source = FALSE), envir) :
object 'y' not found

Also tried this, but y will not change:

ggplot(df, aes(x, x)) +
  geom_point() +
  labs(title = str_c('{closest_state}, another_var: ', df$y)) +
  transition_states(x,
                    transition_length = 0.1,
                    state_length = 0.1)

Another option is to map y as the states level variable and use the frame variable instead of x, but in my application y is either a not-necessarily-unique character variable like above, or it is a numeric variable but again not-necessarily-unique and not-necessarily-ordered. In which case gganimate (or ggplot?) will order it as it sees fit, making the final result weird not ordered by x:

ggplot(df, aes(x, x)) +
  geom_point() +
  labs(title = '{frame}, another_var: {closest_state}') +
  transition_states(y,
                    transition_length = 0.1,
                    state_length = 0.1)

So how to simply add the changing value of the un-ordered, not numeric, y variable?

Finally: This question was asked here but without a reproducible example so it was not answered, hoping this one is better.

Answer 1

One dirty solution would be to paste together the variables and make a new one to use in the transition_states:

df <- mutate(df, title_var = factor(paste(x, y, sep="-"), levels = paste(x, y, sep="-")))
# # A tibble: 6 x 3
# x y     title_var
# <int> <chr> <fct>    
# 1     1 a     1-a      
# 2     2 a     2-a      
# 3     3 b     3-b      
# 4     4 d     4-d      
# 5     5 c     5-c      
# 6     6 a     6-a  

Then we could use gsub() in ordet to strip closest_state from the unwanted part, like this:

gsub(pattern = "\\d+-", replacement = "", "1-a") 
"a"

So:

ggplot(df, aes(x, x)) +
  geom_point() +
  labs(title = '{gsub(pattern = "\\d+-", replacement = "", closest_state)}') +
  transition_states(title_var, transition_length = 0.1, state_length = 0.1)