plotnine.geoms.geom_abline

class plotnine.geoms.geom_abline(mapping: Aes | None = None, data: DataLike | None = None, **kwargs: Any)

Lines specified by slope and intercept

Usage

geom_abline(mapping=None, data=None, stat='identity', position='identity',
            na_rm=False, inherit_aes=False, show_legend=None, raster=False,
            **kwargs)

Only the data and mapping can be positional, the rest must be keyword arguments. **kwargs can be aesthetics (or parameters) used by the stat.

Parameters:

mappingaes, optional

Aesthetic mappings created with aes(). If specified and inherit.aes=True, it is combined with the default mapping for the plot. You must supply mapping if there is no plot mapping.

Aesthetic	Default value
intercept
slope
alpha	1
color	'black'
group
linetype	'solid'
size	0.5

The bold aesthetics are required.

datadataframe, optional

The data to be displayed in this layer. If None, the data from from the ggplot() call is used. If specified, it overrides the data from the ggplot() call.

statstr or stat, optional (default: stat_identity)

The statistical transformation to use on the data for this layer. If it is a string, it must be the registered and known to Plotnine.

positionstr or position, optional (default: position_identity)

Position adjustment. If it is a string, it must be registered and known to Plotnine.

na_rmbool, optional (default: False)

If False, removes missing values with a warning. If True silently removes missing values.

inherit_aesbool, optional (default: False)

If False, overrides the default aesthetics.

show_legendbool or dict, optional (default: None)

Whether this layer should be included in the legends. None the default, includes any aesthetics that are mapped. If a bool, False never includes and True always includes. A dict can be used to exclude specific aesthetis of the layer from showing in the legend. e.g show_legend={'color': False}, any other aesthetic are included by default.

rasterbool, optional (default: False)

If True, draw onto this layer a raster (bitmap) object even ifthe final image is in vector format.

Examples

import pandas as pd
import numpy as np

from plotnine import (
    ggplot,
    aes,
    geom_point,
    labs,
    geom_abline,
    facet_grid
)
from plotnine.data import mpg

AB line

geom_abline() draws a line when the yintercept and gradient is supplied, and is useful as a guide.

# inspect the data
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_abline() with some data, so we start with a basic scatter plot:

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

<Figure Size: (640 x 480)>

Now layer a line over the scatter plot using geom_abline(). geom_abline() requires inputs for the slope (default slope is 1) and y-intercept (default value is [0,0]).

(
    ggplot(mpg, aes(x='displ', y='hwy'))
    + geom_point()
    + geom_abline(intercept=45, # set the y-intercept value
                  slope=-5      # set the slope value
                 )
    + labs(x='displacement', y='horsepower')
)

<Figure Size: (640 x 480)>

You can plot two lines on one plot:

(
    ggplot(mpg, aes(x='displ', y='hwy'))
    + geom_point()
    + geom_abline(intercept=[45,45], # add many lines to a plot using a list for the y-intercepts...
                  slope=[-5,-7]      # ... and for the slopes
                 )
    + labs(x='displacement', y='horsepower')
)

<Figure Size: (640 x 480)>

You can change the look of the line:

(
    ggplot(mpg, aes(x='displ', y='hwy'))
    + geom_point()
    + geom_abline(intercept=45,
                  slope=-5,
                  color='blue',      # set line colour
                  size=2,            # set line thickness
                  linetype="dashed"  # set line type
                 )
    + labs(x='displacement', y='horsepower')
)

<Figure Size: (640 x 480)>

geom_abline() can be used with a facet plot:

(
    ggplot(mpg, aes(x='displ', y='hwy'))
    + geom_point()
    + geom_abline(intercept=45,slope=-5)     # add a line ...
    + facet_grid('drv ~ .')                  # ... to a facet plot.
    + labs(x='displacement', y='horsepower')
)

<Figure Size: (640 x 480)>