Vega-lite: Changes uncovered by Altair 4

[jakevdp]

In https://github.com/altair-viz/altair/pull/1818 I begun the process of making Altair wrappers for Vega-Lite 4.0.0-beta.12. This introduced a couple test failures in examples due to properties that are no longer allowed by the schema.

To add back

• [x] https://altair-viz.github.io/gallery/ridgeline_plot.html fails because bounds is no longer an allowed property of TopLevelUnitSpec.

  • Ham: this one we should add back.

• [x] Any charts that use width or height in the view configuration break, because they are no longer allowed properties of ViewConfig

  • Ham: this one we should add back, perhaps as deprecated configs.

Need to decide whether we want to add these back

• [ ] https://altair-viz.github.io/gallery/anscombe_plot.html and several others fail because columns is no longer an allowed property of TopLevelUnitSpec.

• [ ] https://altair-viz.github.io/gallery/beckers_barley_trellis_plot.html fails because rangeStep is no longer an allowed property of Scale.

• [ ] Similarly, https://altair-viz.github.io/gallery/layered_chart_bar_mark.html fails because rangeStep is no longer an allowed property of ScaleConfig

This is the extent of the issues that came up in a first pass!

[kanitw]

I'm adding bounds and config.view.width/height back in https://github.com/vega/vega-lite/pull/5624.

However, I don't think we should do columns as it's much better to specify: alt.Facet('Series', columns=2).

[kanitw]

For rangeStep, width.step is also a much better syntax, so I slightly prefer not to add it back.

[jakevdp]

Thanks!

[kanitw]

:)

[jakevdp]

One question: currently altair's default theme uses config.width/config.height. Would you prefer me to change that to config.continuousWidth/continuousHeight in V4, to move away from deprecated configs?

[kanitw]

Yes, please. :)

[jakevdp]

Great! Already done in https://github.com/altair-viz/altair/commit/0ccd2e4a8c59f9fa5a1009ed4716bd6882187d01

[eharkins]

Changing scale.rangeStep to width.step in Altair version 4.0.1 caused this for me:

Error: Unrecognized signal name: "x_step"
    at Object.error (/home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-util/build/vega-util.js:22:11)
    at Scope$1.prototype$1.getSignal (/home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-parser/build/vega-parser.js:3342:16)
    at /home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-parser/build/vega-parser.js:84:65
    at Array.forEach (<anonymous>)
    at parseExpression (/home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-parser/build/vega-parser.js:82:17)
    at Scope$1.prototype$1.parseLambdas (/home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-parser/build/vega-parser.js:3360:15)
    at parseSpec (/home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-parser/build/vega-parser.js:2972:11)
    at parseMark (/home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-parser/build/vega-parser.js:2136:13)
    at parseAxis (/home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-parser/build/vega-parser.js:2934:12)
    at /home/eharkins/miniconda2/envs/altairtest2/lib/vega-cli/node_modules/vega-parser/build/vega-parser.js:2960:44

[domoritz]

@eharkins Can you send us the Vega-Lite spec?

[eharkins]

@domoritz Here it is with width.step (as output by chart.save(format="json")):

{
  "config": {
    "view": {
      "continuousWidth": 400,
      "continuousHeight": 300
    }
  },
  "layer": [
    {
      "data": {
        "name": "data-b5d82698a6af51f8073087a9d6f6c082"
      },
      "mark": "rect",
      "encoding": {
        "x": {
          "type": "ordinal",
          "field": "x"
        }
      }
    },
    {
      "data": {
        "name": "data-bc8e995691956dedcd24653f7761f783"
      },
      "mark": "tick",
      "encoding": {
        "x": {
          "type": "ordinal",
          "field": "position"
        }
      },
      "width": {
        "step": 3
      }
    }
  ],
  "$schema": "https://vega.github.io/schema/vega-lite/v4.0.2.json",
  "datasets": {
    "data-b5d82698a6af51f8073087a9d6f6c082": [
      {
        "0": 0
      }
    ],
    "data-bc8e995691956dedcd24653f7761f783": [
      {
        "position": 0
      }
    ]
  }
}

[domoritz]

Can you create a minimal example that shows the issue?

[eharkins]

Yes @domoritz I'll try stripping things down until it's as bare of an altair chart as possible that still gets the error with width.step. Thanks for your response!

[eharkins]

@domoritz I updated the above spec to a minimal example. I'm almost positive that it's because I added width.step to one sub layer of the chart and then added it to another chart in altair using + in python. If I move width.step to the top level LayerChart resulting from the +, the error goes away.

So maybe it's just a matter of adding a helpful message for width.step like this one for chart.background:

ValueError: Objects with "background" attribute cannot be used within LayerChart. Consider defining the background attribute in the LayerChart object instead.

[domoritz]

I don't get an error in the Vega editor try me. Could it be that the issue is fixed in the latest VL version?

[eharkins]

Yes it could be. It seems like Altair 4.0.1 is using VegaLite 4.0.2 and there have been subsequent releases of VegaLite so perhaps one of those contains a fix for this.

[jakevdp]

The current release of Altair uses Vega-Lite 4.0.2, so it's possible that errors you see in Altair output won't reproduce in the Vega editor (which I believe is at 4.4 at the moment)