ggplot x axis expansion not consistent with facets-CodePudding

I have some data I would like to display with a ggplot. The data has several groups (5 in this example), each group containing a variable number of subgroups.

# consistent simulation results
set.seed(1)

# packages
library(dplyr)
library(ggplot2)

# data
data.frame(group=c("group A",
                   rep("group B",2),
                   rep("group C",3),
                   rep("group D",4),
                   rep("group E",5)),
           subgroup=c("a",
                      "a","b",
                      "a","b","c",
                      "a","b","c","d",
                      "a","b","c","d","e"),
           var=rnorm(15,50,10))->data

I want to display these data with subgroup on the x-axis and facets for each group

data%>%
  ggplot(aes(x=subgroup,
             y=var)) 
    geom_col() 
    facet_grid(.~group,
               scales="free",
               space="free")->p

plot p looks like this: no expansion. Now I want to give a little space around group A, so I used scale_x_discrete(expand=expansion(mult=n)) trying various number for n

p scale_x_discrete(expand=expansion(mult=0.1)) labs(title=0.1)
p scale_x_discrete(expand=expansion(mult=0.2)) labs(title=0.2)
p scale_x_discrete(expand=expansion(mult=0.5)) labs(title=0.5)
p scale_x_discrete(expand=expansion(mult=0.7)) labs(title=0.7)
p scale_x_discrete(expand=expansion(mult=1)) labs(title=1)

Which gave me some interesting outputs:

Is there a way to make the spacing for each facet consistent? It seems like there is variable behavior in each facet depending on the number of bars present?

CodePudding user response：

It seems like there is variable behavior in each facet depending on the number of bars present?

That's what multiplicative expansion does. It multiplies the range - if you multiply a small range (1 or 2 bars) it pads by a little bit, if you multiply a big range (10 bars) it pads by a lot.

Is there a way to make the spacing for each facet consistent?

Yes, use additive expansion (expansion(add = X)) not multiplicative (expansion(mult = X)).

Generally, additive expansion makes more sense for discrete scales, and multiplicative expansion makes more sense for continuous scales. This is reflected in the defaults, from ?discrete_scale

The defaults are to expand the scale by 5% on each side for continuous variables, and by 0.6 units on each side for discrete variables.

This add = 0.6 default is what you show in the "no expansion" picture.