VegaLite vlplot basic usage, encoding

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1

I’m new to both Vega Lite and VegaLite.jl, and I’m confused about exactly how is vlplot supposed to work. The VegaLite documentation seems to consist mostly of examples and lacks a more systematic approach to documentation, so I’m having a hard time figuring out the thing that’s confusing me here. (The @vlplot macro is confusing me even more than vlplot, because it doesn’t use Julia syntax, so I would prefer not to use it.)

This is the first example for the “Point” Vega Lite “mark” in the docs, it plots a dot plot:

{
  "data": {"url": "data/movies.json"},
  "mark": "point",
  "encoding": {
    "x": {"field": "IMDB Rating", "type": "quantitative"}
  }
}

This is my initial snippet, basically an attempt at a straightforward adaptation of the dot plot example from Vega Lite to vlplot:

using IndexedTables, VegaLite
data = Float64[3.3, 3.4, 3.41, 3.9]
tab = table((index = (1:length(data)), values = data), pkey=:index, presorted=true)
pl = vlplot(data = tab, mark = :point, encoding = (x = (field = :values, type = :quantitative)))

The above produces just a single dot instead of dot plot, even though it seems like it should “naturally” work. But the below correction works as expected:

pl = vlplot(data = tab, mark = :point, x = (field = :values, type = :quantitative))

From this I would conclude that a Vega Lite encoding has to be specified “inline” in VegaLite.jl, except that the VegaLite documentation actually has some examples where @vlplot is given an encoding argument just like here. (E.g., here: The @vlplot command · VegaLite.jl)

So I don’t really get what’s wrong with my initial example. Can somebody help me understand?

2

Your assumption that function vlplot can just be used instead of macro @vlplot is wrong. The docs Home · VegaLite.jl don’t mention the function at all, so it’s clearly recommended to use the macro.
With that translation is straightforward, at least for this simple example:

pl = @vlplot(
	data = tab, 
	mark = :point, 
	encoding = {
		x = {
			field = :values, 
			type = :quantitative
		}
	}
)
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