Altair

Update includes full compatibility with version 3.3 of Vega-Lite.

Enhancements

- Added support for [vega themes](https://github.com/vega/vega-themes) via `alt.themes.enable(theme_name)` (#1539)

- Added an `alt.renderers.disable_max_rows()` method for disabling the maximum rows check (1538)

- Improved user-facing warnings/errors around layering and faceting (1535).

- `data` argument is now properly handled by `Chart.properties` (1525)

- Compound charts (layer, concat, hconcat, vconcat) now move data to the top level by default. In particular, this means that the `facet()` method can now be called directly on a layered chart without having to change how data is specified. (1521)

- `alt.LayerChart` now supports `mark_*()` methods. If a layer specifies a mark at the top level, all child charts will inherit it (unless they override it explicitly).

- `alt.Chart.facet()` now handles wrapped facets; for example: `chart.facet('column_name', columns=5)` See `altair/examples/us_population_over_time_facet.py` for a more complete example.

Bug fixes

- Make `chart.serve()` and `chart.save()` respect the data transformer setting (1538)

- Fixed a deserialization bug for certain chart specs in schemapi (1543)

Backward-Incompatible Changes

- `alt.Chart.facet()` now accepts a wrapped facet encoding as a first positional argument, rather than a row encoding. The following are examples of old invocations, and the equivalent new invocations:

- `chart.facet(row='col1', column='col2')`: unchanged
- `chart.facet('col1', 'col2')`: change to `chart.facet(row='col1', column='col2')`
- `chart.facet('col1')`: change to `chart.facet(row='col1')`

In each case, the new invocations are compatible back to Altair 2.X.

- Several of the encoding channels added in 3.0 have had their capitalization corrected to better match the names used in the schema:

- `alt.Fillopacity` -> `alt.FillOpacity`
- `alt.Strokeopacity` -> `alt.StrokeOpacity`
- `alt.Strokewidth` -> `alt.StrokeWidth`
- `alt.Xerror` -> `alt.XError`
- `alt.Xerror2` -> `alt.XError2`
- `alt.Yerror` -> `alt.YError`
- `alt.Yerror2` -> `alt.YError2`

Fix version info bug for HTML output and Colab & Kaggle renderers.

Update to Vega-Lite 3.2 and Vega 5.3 & support all new features. See
https://github.com/vega/vega-lite/releases/tag/v3.0.0 for Vega-Lite
feature lists.

Highlights

- new compound marks: `mark_boxplot()`, `mark_errorband()`, `mark_errorbar()`
- new transforms: `transform_impute()`, `transform_joinaggregate()`, `transform_flatten()` `transform_fold()`, `transform_sample()`, `transform_stack()`
- new `facet` encoding that is similar to the `row` and `column` encoding, but allows for wrapped facets
- new `alt.concat()` function that is similar to `alt.hconcat` and `alt.vconcat`, but allows for more general wrapped concatenation
- new `columns` keyword that allows wrapped faceting, repeating, and concatenation.
- many, many bug fixes
- tooltips can now be automatically populated using the `tooltip` mark configuration.
- ability to specify initial conditions for selections

Enhancements

- Several documentation cleanups & new examples

Bug Fixes

- Fix incompatibility with pandas version 0.24 (1315)

Includes many reworked examples in the example gallery.

Enhancements

- Better errors for non-string column names, as well as automatic conversion of `pandas.RangeIndex` columns to strings (1107)
- Renderers now have `set_embed_options()` method (1203)
- Added kaggle renderer & more HTML output options (1123)


Maintenance

- fix typing requirement in Python 3.6+ (1185)
- Added support & CI testing for Python 3.7 (1008)

Bug fixes

- Selection predicates now recognize all valid entries (1143)
- Python 2 support for `chart.save()` (1134)

Bug Fixes

- fix missing JSON resource in `altair.vega.v4` (1097)