Data transformations

Vega-Lite provides several data transformations using the transform property. Any arbitrary data transformation supported by Vega-Lite can be created in Deneb.jl using Transform, e.g.:

using Deneb
Transform(
    aggregate=[(field=:Acceleration, op=:mean, as=:mean_acc)],
    groupby=[:Cylinders],
)

Deneb.TransformSpec: 
[
  {
    "aggregate": [
      {
        "field": "Acceleration",
        "op": "mean",
        "as": "mean_acc"
      }
    ],
    "groupby": [
      "Cylinders"
    ]
  }
]

creates a Deneb.TransformSpec that contains the subspec for the transform property of an aggregate transformation.

The method above is rather verbose, Deneb.jl provides a number of convenient transform_* methods that facilitate the creation of data transformation subspecs. The previous aggregate transformation example could more conveniently be created using the transform_aggregate method.

transform_aggregate(mean_acc="mean(Acceleration)", groupby=:Cylinders)

Deneb.TransformSpec: 
[
  {
    "aggregate": [
      {
        "field": "Acceleration",
        "op": "mean",
        "as": "mean_acc"
      }
    ],
    "groupby": [
      "Cylinders"
    ]
  }
]

Currently Deneb.jl supports the following Vega-Lite data transformation via transform_* convenient methods: