Horizontal line

In [1]:

from plotnine import ggplot, aes, geom_point, geom_hline, facet_grid, labs
from plotnine.data import mpg

geom_hline() draws a vertical line, and is useful as a guide.

In [2]:

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

It’s useful to use geom_hline() with some data, so we start with a basic scatter plot:

In [3]:

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

Now add a horizontal line to the scatter plot:

In [4]:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + geom_hline(yintercept=25)  # add one horizonal line
    + labs(x="displacement", y="horsepower")
)

You can add many horizontal lines:

In [5]:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + geom_hline(yintercept=[25, 35, 45])  # add many horizontal lines using a list
    + labs(x="displacement", y="horsepower")
)

You can change the look of the line:

In [6]:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + geom_hline(
        yintercept=25,
        color="yellow",  # set line colour
        size=2,  # set line thickness
        linetype="dashed",  # set line type
    )
    + labs(x="displacement", y="horsepower")
)

And you can add horizontal lines to a facet plot:

In [7]:

(
    ggplot(mpg, aes(x="displ", y="hwy"))
    + geom_point()
    + geom_hline(yintercept=25)  # add a vertical line...
    + facet_grid("drv")  # ... to a facet plot
    + labs(x="displacement", y="horsepower")
)