Overriding Default Grouping with the `group` Aesthetic#

How Grouping Works in Lets-Plot#

Default Grouping Behavior:

Lets-Plot automatically groups data by discrete variables mapped to aesthetics like color, shape, linetype, etc.
This creates separate visual elements (lines, paths, polygons) for each unique combination of these variables

Explicit Group Control:

Use group = 'var' to group only by that specific variable, overriding default grouping
Use group = [var1, var2, ...] to group by the interaction of multiple variables
Use group = [] to disable all grouping completely

1. Highway MPG by Drive Type#

seed = 21
( ggplot(mtcars, aes(x='drv', y='hwy')) 
  + geom_violin(tooltips='none') 
  + geom_sina(seed=seed)
)

2. Add More Information - `color`#

( ggplot(mtcars, aes(x='drv', y='hwy')) 
  + geom_violin(tooltips='none') 
  + geom_sina(aes(color='cyl'), seed=seed)
)

3. Discrete `color`: Default Grouping Creates Unwanted Separation#

Let’s add discrete colors by marking the cyl variable as discrete.

When we map color=as_discrete('cyl'), Lets-Plot automatically groups the data by the discrete color variable.
This means:

Automatic grouping: Each combination of drv (x-axis) and cyl (color) becomes a separate group
Position adjustment: The geom_sina() uses “dodge” positioning by default, which separates overlapping groups horizontally
Result: Instead of one sina plot per drive type, we get 4 separate sina plots (one for each cylinder count) within each drive type category

( ggplot(mtcars, aes(x='drv', y='hwy')) 
  + geom_violin(tooltips='none') 
  + geom_sina(aes(color=as_discrete('cyl')), seed=seed)
)

4. Fix with Explicit Grouping by Drive Type#

( ggplot(mtcars, aes(x='drv', y='hwy')) 
  + geom_violin(tooltips='none') 
  + geom_sina(aes(color=as_discrete('cyl'),
                  group='drv' # <-- group only by drive type (ignoring the color variable for grouping)
  ), seed=seed)
)

5. Cleaner Fix: Disable All Grouping#

( ggplot(mtcars, aes(x='drv', y='hwy')) 
  + geom_violin(tooltips='none') 
  + geom_sina(aes(color=as_discrete('cyl'),
                  group=[]  # <-- disable all grouping entirely
  ), seed=seed)
)

	manufacturer	model	displ	year	cyl	trans	drv	cty	hwy	fl	class
i64	str	str	f64	i64	i64	str	str	i64	i64	str	str
1	"audi"	"a4"	1.8	1999	4	"auto(l5)"	"f"	18	29	"p"	"compact"
2	"audi"	"a4"	1.8	1999	4	"manual(m5)"	"f"	21	29	"p"	"compact"
3	"audi"	"a4"	2.0	2008	4	"manual(m6)"	"f"	20	31	"p"	"compact"
4	"audi"	"a4"	2.0	2008	4	"auto(av)"	"f"	21	30	"p"	"compact"
5	"audi"	"a4"	2.8	1999	6	"auto(l5)"	"f"	16	26	"p"	"compact"

Overriding Default Grouping with the group Aesthetic#