plotnine.facet_grid

facet_grid(
    rows=None,
    cols=None,
    *,
    margins=False,
    scales="fixed",
    space="fixed",
    shrink=True,
    labeller="label_value",
    as_table=True,
    drop=True
)

Wrap 1D Panels onto 2D surface

Parameters

rows : Optional[str | Sequence[str]] = None

Variable expressions along the rows of the facets/panels. Each expression is evaluated within the context of the dataframe.

cols : Optional[str | Sequence[str]] = None

Variable expressions along the columns of the facets/panels. Each expression is evaluated within the context of the dataframe.

margins : bool | Sequence[str] = False

variable names to compute margins for. True will compute all possible margins.

space : Literal["fixed", "free", "free_x", "free_y"] | FacetSpaceRatios = "fixed"

Control the size of the x or y sides of the panels. The size also depends to the scales parameter.

If a string, it should be one of ['fixed', 'free', 'free_x', 'free_y'].

If a dict, it indicates the relative facet size ratios such as:

{"x": [1, 2], "y": [3, 1, 1]}

This means that in the horizontal direction, the second panel will be twice the length of the first. In the vertical direction the top facet will be the 3 times longer then the second and third facets.

Note that the number of dimensions in the list must equal the number of facets that will be produced.

shrink : bool = True

Whether to shrink the scales to the output of the statistics instead of the raw data.

labeller : Literal["label_value", "label_both", "label_context"] = "label_value"

How to label the facets. A string value if it should be one of ["label_value", "label_both", "label_context"].

as_table : bool = True

If True, the facets are laid out like a table with the highest values at the bottom-right. If False the facets are laid out like a plot with the highest value a the top-right

drop : bool = True

If True, all factor levels not used in the data will automatically be dropped. If False, all factor levels will be shown, regardless of whether or not they appear in the data.

Examples


from plotnine import ggplot, aes, geom_point, labs, facet_grid, theme, element_text, element_rect
from plotnine.data import mpg

Facet grid

facet_grid() is used to form a grid of plots, where the rows and columns of the grid are set by the faceting variables. It is useful for visualising two discrete variables.

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

Basic scatter plot:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + labs(x="displacement", y="horsepower")
)

Facet a discrete variable into rows:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + facet_grid("drv")
    + labs(x="displacement", y="horsepower")
)

Facet a discrete variable into columns:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + facet_grid(cols="cyl")
    + labs(x="displacement", y="horsepower")
)

Facet two discrete variables into rows and columns:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + facet_grid("drv", "cyl")
    + labs(x="displacement", y="horsepower")
)

To change the plot order of the rows or columns in the facet grid, reorder the levels of the faceting variable in the data.

# re-order categories
mpg["drv"] = mpg["drv"].cat.reorder_categories(["f", "r", "4"])
# facet plot with reorded drv category
(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + facet_grid("drv", "cyl")
    + labs(x="displacement", y="horsepower")
)

You can choose if the scale of x- and y-axes are fixed or variable by using the scales argument within the facet_grid() command:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + facet_grid("drv", scales="free")
    + labs(x="displacement", y="horsepower")
)

You can add additional information to your facet labels, by using the labeller argument within the facet_grid() command. Below we use labeller = 'label_both' to include the column name in the facet label.

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + facet_grid("drv", labeller="label_both")
    + labs(x="displacement", y="horsepower")
)

You can add two discrete variables to a facet:

# add additional column for plotting exercise
mpg["transmission"] = mpg["trans"].map(
    lambda x: "auto" if "auto" in x else "man" if "man" in x else ""
)
# inspect new column transmission which identifies cars as having an automatic or manual transmission
mpg.head()
manufacturer model displ year cyl trans drv cty hwy fl class transmission
0 audi a4 1.8 1999 4 auto(l5) f 18 29 p compact auto
1 audi a4 1.8 1999 4 manual(m5) f 21 29 p compact man
2 audi a4 2.0 2008 4 manual(m6) f 20 31 p compact man
3 audi a4 2.0 2008 4 auto(av) f 21 30 p compact auto
4 audi a4 2.8 1999 6 auto(l5) f 16 26 p compact auto 
# facet plot with two variables on one facet
(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + facet_grid(["drv", "transmission"])  # use a list to add additional faceting variables
    + labs(x="displacement", y="horsepower")
)

Facet labels can be rotated to make them easier to read using strip_text_y = element_text(angle = 0) for row labels within the theme() command (use strip_text_x = element_text(angle = 0) for column labels).

If the labels do not fit in the strip, adjust the width of the strip using strip_background_y for rows (use strip_background_x for columns). You may also need to adjust the text position so it fits in the strip: adjust the horizontal text position in the strip by specifying ha in element_text()(specify va in element_text() to adjust the vertical text position).

You can also change the colour of the strip by specifying color in element_text() .

(
    ggplot(mpg, aes(x="drv", y="model"))
    + geom_point()
    + facet_grid("manufacturer", scales="free")
    + theme(
        strip_text_y=element_text(angle=0),   # change facet text angle
        strip_background_y=element_rect(fill="#969dff"),   # change background colour of facet background
        figure_size=(6, 15),  # adjust width & height of figure to fit y-axis
    )
    + labs(x="displacement", y="")
)

Source: Facet grid