Data transformation¶
With transforms, you can build a pipeline that modifies the data before the data objects are mapped to mark instances. In an abstract sense, a transformation inputs a list of data items and outputs a list of new items that may be filtered, modified, or generated from the original items.
Departure from Vega-Lite
The notation of transforms is different from Vega-Lite to enable more
straghtforward addition of new operations. Each transform has to be
specified using an explicit type
property like in the lower-level
Vega visualization grammar.
Thus, the transform type is not inferred from the presence of
transform-specific properties.
Example¶
The following example uses the "filter"
transform to retain
only the rows that match the predicate expression.
{
...,
"data": { ... },
"transform": [
{
"type": "filter",
"expr": "datum.end - datum.start < 5000"
}
],
...
}