Stacked barchart, independent fill order for each stack - r

Question

I'm facing a behaviour of ggplot2, ordering and stacked barplot that I cannot understand. I've read some question about it (here,here and so on), but unluckily I cannot find a solution that suits to me. Maybe the answer is easy and I cannot see it. Hope it's not a dupe.
My main goal is to have each stack ordered independently, based on the ordering column (called here ordering).
Here I have some data:
library(dplyr)
library(ggplot2)
dats <- data.frame(id = c(1,1,1,2,2,3,3,3,3),
value = c(9,6,4,5,6,4,3,4,5),
ordering = c(1,2,3,2,3,1,3,2,4),
filling = c('a','b','c','b','a','a','c','d','b')) %>% arrange(id,ordering)
So there is an ID, a value, a value to use to order, and a filling, the data are as they should be ordered in the plot, as looking the ordering column.
I tried to plot it: the idea is to plot as a stacked barchart with x axis the id, the value value, filled by filling, but the filling has as order the value of ordering, in an ascending ordering, i.e. biggest value of ordering at the bottom for each column. The ordering of the filling is somewhat equal as the dataset, i.e. each column has an independent order.
As you can imagine those are fake data, so the number of id can vary.
id value ordering filling
1 1 9 1 a
2 1 6 2 b
3 1 4 3 c
4 2 5 2 b
5 2 6 3 a
6 3 4 1 a
7 3 4 2 d
8 3 3 3 c
9 3 5 4 b
When I plot them, there is something I do not understand:
library(dplyr)
dats$filling <- reorder(dats$filling, -dats$ordering)
ggplot(dats,aes(x = id,
y = value,
fill = filling)) +
geom_bar(stat = "identity",position = "stack") +
guides(fill=guide_legend("ordering"))
The second and the third id are not properly ordered, I should have the order of the original dataset.

Answer 1

If you use separate geom_bars, you can make the orders different.
dats %>%
ggplot(aes(x = id, y = value, fill = reorder(filling,-ordering))) +
geom_bar(stat = "identity", position = "stack", data = dats %>% filter(id == 1)) +
geom_bar(stat = "identity", position = "stack", data = dats %>% filter(id == 2)) +
geom_bar(stat = "identity", position = "stack", data = dats %>% filter(id == 3)) +
guides(fill=guide_legend("ordering"))
More generally:
bars <- map(unique(dats$id)
, ~geom_bar(stat = "identity", position = "stack"
, data = dats %>% filter(id == .x)))
dats %>%
ggplot(aes(x = id, y = value, fill = reorder(filling,-ordering))) +
bars +
guides(fill=guide_legend("ordering"))

Answer 2

The problem is that, in your case, different bars should use the same values (levels) of filling in a different order. This conflicts with the way ggplot works: taking the factor levels (which already have a certain order) and applying them in the same way for each bar.
A workaround then is... To create many factor levels.
ggplot(dats, aes(x = id, y = value, fill = interaction(-ordering, id))) +
geom_bar(stat = "identity", position = "stack")
This one now is too "generous" by being too detailed. However, what we can do now is to deal with the legend and the different colors:
dats <- arrange(dats, id, -ordering)
aux <- with(dats, match(sort(unique(filling)), filling))
ggplot(dats, aes(x = id, y = value, fill = interaction(-ordering, id))) +
geom_bar(stat = "identity", position = "stack") +
scale_fill_manual("Ordering", values = scales::hue_pal()(4)[dats$filling],
labels = with(dats, filling[aux]),
breaks = with(dats, interaction(-ordering, id)[aux]))
Here I first rearrange the rows of dats as to avoid doing that later. Then aux is an auxiliary vector
aux
# [1] 3 2 1 8
giving arbitrary positions (one for each) where levels a, b, c, and d (in this order) appear in dats, which again is useful later. Then I simply set corresponding scale values, labels, and breaks... Lastly, I use scales::hue_pal to recover the original color palette.

Answer 3

The problem here is that the element filling = d only appears in the third group with a low value. One solution, could be to fill non-present values with 0:
library(dplyr)
#>
#> Attachement du package : 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
library(ggplot2)
dats <- data.frame(id = c(1,1,1,1,2,2,2,2,3,3,3,3),
value = c(9,6,4,0,5,6,0,0,4,3,4,5),
ordering = c(1,2,3,5,2,3,5,5,1,3,2,4),
filling = c('a','b','c','d','b','a','c','d','a','c','d','b')) %>% arrange(id,ordering)
ggplot(dats,aes(x = id,
y = value,
fill = reorder(filling,-ordering))) +
geom_bar(stat = "identity",position = "stack") +
guides(fill=guide_legend("ordering"))
Created on 2018-12-03 by the reprex package (v0.2.1)