Horizontal bar graphs: Match default stack order in legend as well

[dpprdan]

According to the v2.2.0 announcement: "position_stack() and position_fill() now stack values in the reverse order of the grouping, which makes the default stack order match the legend." IMHO this should also be true for horizontal bar graphs.

df <- data.frame(
  x = factor(c(1, 1, 2, 2)),
  y = c(1, 3, 2, 1),
  grp = c("a", "b", "a", "b")
)

ggplot(data = df, aes((x), y, fill = (grp), label = y)) +
  geom_col() +
  geom_text(position = "stack_point") + 
  theme(legend.position = "bottom") +
  coord_flip()

position = "stack_point" borrowed from #1821.

[hadley]

@thomasp85 we forgot about this important case. Any ideas? forcats::fct_rev() doesn't help as it flips order in both plot and legend.

[thomasp85]

Honestly I don't think we can have it both ways, so we need to decide on the preferred default.

[thomasp85]

We could add a reverse argument to the scale constructors that would make it easy to reverse legend order. An ugly "fix" but it would solve it partly

[hadley]

Would reversing legend order work? It doesn't seem great to have labels "b", "a". And reversing the mapping between colour and letter would just flip the colours in both locations.

[thomasp85]

Come to think of it the natural thing would be to have a switch in position_stack. We cannot make this automatic as neither Coord, Scale, nor Position is aware of each other's presence and it would thus degenerate into horrible coord_flip checks everywhere (we already have enough of those)

[hadley]

Agreed. Let me merge my stacking changes, and then one of us can add a reverse argument.

[hadley]

@thomasp85 I also changed the default order to stack from inside-out (i.e. from close to axis to far away). That looks better to me eye because you get a mirror image if each x value has the same levels.

[thomasp85]

I'm unsure what you mean - skimming the diff it seems default behaviour is preserved (I.e. Stacking from top to bottom)

[hadley]

Negative values stack in the opposite direction now