R, ggplot2, limit rows in a faceted barplot - r

Question

Sup,
Consider the following lines:
data
df=data.frame(
prod=sample(1:30, 1000, replace=TRUE),
mat=sample(c('yes', 'no'), 1000, replace=TRUE),
fj=sample(c(1,2), 1000, replace = TRUE)
)
plot
df %>%
group_by(mat, prod, fj) %>%
summarise(n = n()) %>%
arrange(desc(n)) %>%
slice(1:5) %>%
ggplot(aes(x = reorder(prod, n), y = n)) +
geom_col(fill = RColorBrewer::brewer.pal(3, 'Dark2')[2], colour = "grey", alpha = 0.8) +
labs(x = "Prod", y = "Qnt") +
scale_y_continuous(labels = scales::comma) +
coord_flip() +
facet_wrap(fj ~ mat, scale="free") +
theme_minimal()
which gives me
Now, if i drop fj variable, as in
df %>%
group_by(mat, prod) %>%
summarise(n = n()) %>%
arrange(desc(n)) %>%
slice(1:5) %>%
ggplot(aes(x = reorder(prod, n), y = n)) +
geom_col(fill = RColorBrewer::brewer.pal(3, 'Dark2')[2], colour = "grey", alpha = 0.8) +
labs(x = "Prod", y = "Qnt") +
scale_y_continuous(labels = scales::comma) +
coord_flip() +
facet_wrap(~ mat, scale="free") +
theme_minimal()
slice(1:5) does it's job and i've got:
Question
why slice and reorder doesn't seems to work properly when there's 3+ variables and what should i do to limit the first plot to 5 lines each?

Answer 1

When you call summarize you loose one level of grouping. In this case, you lost fj, so when you slice it's not included in the group divisions.
If you first ungroup then group_by mat and fj, I think you'll end up with what you are looking for.
df %>%
group_by(mat, prod, fj) %>%
summarise(n = n()) %>%
ungroup()%>%
group_by(mat, fj) %>%
arrange(desc(n)) %>%
slice(1:5) %>%
ggplot(aes(x = reorder(prod, n), y = n)) +
geom_col(fill = RColorBrewer::brewer.pal(3, 'Dark2')[2], colour = "grey", alpha = 0.8) +
labs(x = "Prod", y = "Qnt") +
scale_y_continuous(labels = scales::comma) +
coord_flip() +
facet_wrap(fj ~ mat, scale="free") +
theme_minimal()
This leaves the problem of reordering the prod variable within each facet. It doesn't work in the example above because you are ordering by the entire data frame, and some of the values of Prod are repeated in several of the facets. As discussed in this blog post by #drsimonj you need to create an order variable and plot based on that. This follows/blatently copies the method outlined in the blog post.
df %>%
group_by(mat, prod, fj) %>%
summarise(n = n()) %>%
group_by(mat, fj) %>%
arrange(desc(n)) %>%
slice(1:5) %>%
ungroup() %>%
arrange(fj,mat, n) %>% # arrange the entire table by the facets first, then by the n value
mutate(row.order = row_number()) %>% # create dummy variable
ggplot(aes(x = row.order, y = n)) + # plot by the dummy variable
geom_col(fill = RColorBrewer::brewer.pal(3, 'Dark2')[2], colour = "grey", alpha = 0.8, position = "dodge") +
labs(x = "Prod", y = "Qnt") +
scale_y_continuous(labels = scales::comma) +
scale_x_continuous( # add back in the Prod values
breaks = df2$row.order,
labels = df2$prod
)+
coord_flip() +
facet_wrap(fj ~ mat, scales = "free") +
theme_minimal()