readme.md
In vegawidget: 'Htmlwidget' for 'Vega' and 'Vega-Lite'

This example shows how we can design a chart using Vega-Lite, then use Shiny to run that chart, varying the data. The example uses a dataset with a single observation, a point constrained to the unit-circle. The angle of the point is controlled with a slider-input.

In the server function, we create a reactive data-frame, rct_data() that converts the angle-input into a set of coordinates. We use vw_shiny_set_data(), which acts as a Shiny observer, to update the chart's dataset in response to changes in the reactive expression rct_data(). To do this, we had to name the dataset in the Vega-Lite specification; you will see in the definition of spec_circle that there is a dataset named "source". We use this as the name argument for vw_shiny_set_data().

Also in the server function, we have a function vw_shiny_get_data(), which acts as a Shiny reactive that returns a data.frame. We supply this function with the name of the dataset in the chart; Vega and Shiny will supply new values of the dataset as it changes in the Vega chart.