v0.8.0 – Migrating to Vega 2

Syntax Change

• axis
  • only include axis.orient when necessary
• legends
  • set legend's orient to right by default (similar to Vega)
  • Vega-lite now supports multiple legends
• filter
  • move filter to data.filter and takes Vega expression as parameter instead of a complicated predicate object.
  • Null filter is added before binning and timeUnit conversion
• scale
  • scale.reverse is removed as it is redundant with sort.
• stack
  • add stack control to color and detail encoding
• sort — now sort property can be either undefined, a String or an Object
  • undefined - the field is unsorted.
  • (as String) 'ascending' or 'descending' – the field is sort by the field's value in ascending or descending order.
  • (as Object — for ordinal/nominal fields only) A sort field object - for sorting the field by an aggregate calculation (sort.op) over a specified sort field (sort.field) in a specified order (sort.order)

Vega 2 Migration Refactor

• ValueRef
  • replace d.data with datum in filter
  • add datum. option to fieldRef and use it in time transform and template
  • eliminate outdated fieldRef options
  • Replace the eliminated group mark properties with field.group
  • Refer to {group: 'mark.group.width’} with
• Transforms
  • Aggregation, Bin
  • Stack
    • Use vega2 stack's parameter and rename it to <field_name>_start|end, remove the need to add facet transform before stacking
    • Make facet comes after stack for stacked area chart (This makes stacked area chart looks almost right but still looks weird due to #307 – see example screenshot)
  • Facet
    • use field name reference instead of using keys.0 (#639)
• Aggregation (#621)
  • avg => mean
  • add all supported aggregation in Vega 2
• Sorting (#612)
  • remove sort.js and no longer use sort-<field_name> tables as data source
  • modify scale.domain() to include DataRef’s .sort object
  • modify sort property to be consistent with Vega 2 (but still leave it as a top-level vega-lite property)
    • sort.name => sort.field
    • sort.aggregate => sort.op

API Change

• vl.field => vl.encDef, field.js => encDef.js

Internal Refactor

Variable Name

• fieldName => field
• field => encDef

Other

• update vega dependency in editor and gallery to Vega 2
• removed _vega2 flag
• extract filter non-positive value when log are presented from normal filter
• eliminate encoding.fieldName() and just use encoding.field(...).name
• only use encDef.name where applicable rather than calling fieldRef
• local variable refactor in scale.js
• move stack’s stacked data transform to data.stack
• add encoding.stack so we do not have to pass stack around
• remove Encoding.toggleFilterNullO, which should just be a part of vega-lite-ui

Examples

• added Aggregate Bar Chart, Stacked bar chart, Trellis Stacked Bar Chart
• both vl input and vg output are validated in the gallery and editor