Compound Charts¶

Altair provides a concise API for creating multi-panel and layered charts, and we’ll mention three of them explicitly here:

Layering
Horizontal Concatenation
Vertical Concatenation
Repeat Charts

We’ll explore those briefly here.

import altair as alt

Layering¶

Layering lets you put layer multiple marks on a single Chart. One common example is creating a plot with both points and lines representing the same data.

Let’s use the stocks data for this example:

from vega_datasets import data
stocks = data.stocks()
stocks.head()

	symbol	date	price
0	MSFT	2000-01-01	39.81
1	MSFT	2000-02-01	36.35
2	MSFT	2000-03-01	43.22
3	MSFT	2000-04-01	28.37
4	MSFT	2000-05-01	25.45

Here is a simple line plot for the stocks data:

alt.Chart(stocks).mark_line().encode(
    x='date:T',
    y='price:Q',
    color='symbol:N'
)

and here is the same plot with a circle mark:

alt.Chart(stocks).mark_circle().encode(
    x='date:T',
    y='price:Q',
    color='symbol:N'
)

We can layer these two plots together using a + operator:

lines = alt.Chart(stocks).mark_line().encode(
    x='date:T',
    y='price:Q',
    color='symbol:N'
)

points = alt.Chart(stocks).mark_circle().encode(
    x='date:T',
    y='price:Q',
    color='symbol:N'
)

lines + points

This + is just a shortcut to the alt.layer() function, which does the same thing:

alt.layer(lines, points)

One pattern we’ll use often is to create a base chart with the common elements, and add together two copies with just a single change:

base = alt.Chart(stocks).encode(
    x='date:T',
    y='price:Q',
    color='symbol:N'
)

base.mark_line() + base.mark_circle()

Horizontal Concatenation¶

Just as we can layer charts on top of each other, we can concatenate horizontally using alt.hconcat, or equivalently the | operator:

base.mark_line() | base.mark_circle()

alt.hconcat(base.mark_line(),
            base.mark_circle())

This can be most useful for creating multi-panel views; for example, here is the iris dataset:

iris = data.iris()
iris.head()

	sepalLength	sepalWidth	petalLength	petalWidth	species
0	5.1	3.5	1.4	0.2	setosa
1	4.9	3.0	1.4	0.2	setosa
2	4.7	3.2	1.3	0.2	setosa
3	4.6	3.1	1.5	0.2	setosa
4	5.0	3.6	1.4	0.2	setosa

base = alt.Chart(iris).mark_point().encode(
    x='petalWidth',
    y='petalLength',
    color='species'
)

base | base.encode(x='sepalWidth')

Vertical Concatenation¶

Vertical concatenation looks a lot like horizontal concatenation, but using either the alt.hconcat() function, or the & operator:

base & base.encode(y='sepalWidth')

Repeat Chart¶

Because it is such a common pattern to horizontally and vertically concatenate charts while changing one encoding, Altair offers a shortcut for this, using the repeat() operator.

import altair as alt
from vega_datasets import data

iris = data.iris()

fields = ['petalLength', 'petalWidth', 'sepalLength', 'sepalWidth']

alt.Chart(iris).mark_point().encode(
    alt.X(alt.repeat("column"), type='quantitative'),
    alt.Y(alt.repeat("row"), type='quantitative'),
    color='species'
).properties(
    width=200,
    height=200
).repeat(
    row=fields,
    column=fields[::-1]
).interactive()

This repeat API is still not as streamlined as it could be, but we’ll be working on that.

Altair Tutorial

Compound Charts¶

Layering¶

Horizontal Concatenation¶

Vertical Concatenation¶

Repeat Chart¶