Make individual colors from Vega color schemes accessible from Altair

[joelostblom]

Tasks

• Open upstream issue to work out API (https://github.com/vega/vega)

Description

I think it would be valuable to make all the individual colors from Vega schemes accessible programmatically from Altair. Since Vega stores them in a single file, we could parse that and create a Python dictionary that could be used to access single colors from each color scheme. Something like this:

Code block

pd.read_table(
    'https://raw.githubusercontent.com/vega/vega/v5.21.0/packages/vega-scale/src/palettes.js',
    skipinitialspace=True,
    sep=':',
).drop(
    index=['export const discrete = {', '};']
).iloc[:, 0].str.replace(
    "'", ""
).str.replace(
    ',', ''
).apply(
    lambda x: ["#" + x[i:i+6] for i in range(0, len(x), 6)]
).to_dict()

{'blues': [
  '#cfe1f2',
  '#bed8ec',
  '#a8cee5',
  '#8fc1de',
  '#74b2d7',
  '#5ba3cf',
  '#4592c6',
  '#3181bd',
  '#206fb2',
  '#125ca4',
  '#0a4a90'],
 'greens': [
  '#d3eecd',
  '#c0e6ba',
  '#abdda5',
  '#94d391',
  '#7bc77d',
  '#60ba6c',
  '#46ab5e',
  '#329a51',
  '#208943',
  '#0e7735',
  '#036429']
...

[dangotbanned]

@joelostblom I'm adding some context for what is going on in your script, and linking docs for Vega/Color Schemes

The lambda appears to be similar to d3-scale-chromatic/src/colors.js, with an example of usage in category10.js.
In short, splitting a string containing multiple hexadecimal colors

src/categorical/category10.js

https://github.com/d3/d3-scale-chromatic/blob/2c52792197299346b7bdb94322bb4dff8f554fea/src/categorical/category10.js#L3

A related comment by @domoritz (vega/vega#3843 (comment))

import colors from "../colors.js";

export default colors("1f77b4ff7f0e2ca02cd627289467bd8c564be377c27f7f7fbcbd2217becf");

The current palettes.js has changed since this issue was opened.
Lines L1-L12 and L78-L94 would probably break the initial parser idea.

I do agree these would be nice to have available in altair.
I think we should try to push for a Public API for this upstream in (https://github.com/vega/vega) - since that would be safer than dependending on internal library code.
That route was really help for me when I started reaching for vl_convert internals in vega/vl-convert#191

[joelostblom]

I think we should try to push for a Public API for this upstream in (https://github.com/vega/vega) - since that would be safer than dependending on internal library code.

Yes, I agree that this is the better option