Altair: Selecting a color from a Vega color scheme for plot

user_18092798 0
Viewed 1012

So I know that you can select colors in an Altair plot by setting color='blue' or by specifying a hex code. I was wondering if it's possible to instead use a single color from a Vega color scheme like dark2 or set1 without explicitly specifying its hex code.

I want it be something like:


color = sample_from_scheme('set1')

alt.Chart(df).mark_circle().encode(
    x='X',
    y='Y',
    color=color
).save(
    "image.html"
)
altair plot python
2 Answers

Scheme names are evaluated in the Javascript renderer; there is currently no way to access the colors represented by scheme names from within Python.

You can see where the color schemes are defined in Vega's javascript source here: https://github.com/vega/vega/blob/v5.21.0/packages/vega-scale/src/palettes.js

So, for example, set1 consists of ['e41a1c', '377eb8', '4daf4a', '984ea3', 'ff7f00', 'ffff33', 'a65628', 'f781bf', '999999']

user_29378310

You could access a single color from the Vega color schemes by parsing the color scheme source file from the Vega repo:

color_scheme = 'set1'
color_number = 0

color = pd.read_table(
    'https://raw.githubusercontent.com/vega/vega/v5.21.0/packages/vega-scale/src/palettes.js',
    skipinitialspace=True,
    sep=':',
).loc[
    color_scheme
].str.replace(
    "'",
    ""
).str.replace(
    ",",
    ""
).apply(
    lambda x: ["#" + x[i:i+6] for i in range(0, len(x), 6)]
)[0][color_number]

color

Output:

'#e41a1c'

You can see all colors by going to https://vega.github.io/vega/docs/schemes/ and hovering the names in case you want to confirm.

user_21668230
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