Issue with AlgebraOfGraphics.jl: MethodError when using data(df)

General Usage
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1

I’m trying to plot timing data using AlgebraOfGraphics.jl and CairoMakie.jl. My data consists of timestamps (in seconds) and hit types (early, perfect, late). The hit types are mapped to numeric values:

  • "early" → -1.0
  • "perfect" → 0.0
  • "late" → 1.0

I create a DataFrame from the data and pass it to data(df), but I keep getting a MethodError. Here’s my code:

using AlgebraOfGraphics
using CairoMakie
using DataFrames

function load_json(filepath)
    open(filepath, "r") do file
        return JSON.parse(file)
    end
end

function process_data(json_data)
    times = []
    hit_types = []
    
    for entry in json_data
        for miss in entry["Details"]["miss"]
            time = miss["time"]
            offset = entry["Details"]["offset"]
            
            if offset < 0
                hit_type = "early"
            elseif offset == 0
                hit_type = "perfect"
            else
                hit_type = "late"
            end
            
            push!(times, time)
            push!(hit_types, hit_type)
        end
    end
    println(times)
println(hit_types)

    return times, hit_types
end

function plot_hits(times, hit_types)
    hit_mapping = Dict("early" => -1.0, "perfect" => 0.0, "late" => 1.0)
    hit_nums = [hit_mapping[hit] for hit in hit_types]

    times_clean = Float64.(collect(times))
    hit_nums_clean = Float64.(collect(hit_nums))

    df = DataFrame(time=times_clean, hit_type=hit_nums_clean)

    column_table = Tables.columntable(df)
    spec = data(column_table) * mapping(:time, :hit_type) * visual(Lines)

    spec |> draw
end

json_filepath = "Implementierung/src/return.json"
json_data = load_json(json_filepath)
times, hit_types = process_data(json_data)
plot_hits(times, hit_types)

The DataFrame looks fine:
10×2 DataFrame
Row │ time hit_type
─────┼───────────────────
1 │ 0.0 0.0
2 │ 15.0 1.0
3 │ 8.0 1.0
4 │ 14.0 1.0
5 │ 6.0 1.0
6 │ 10.0 1.0
7 │ 7.0 1.0
8 │ 12.0 1.0
9 │ 15.0 1.0
10 │ 9.0 1.0

When I run the function, I get the following error:

ERROR: MethodError: objects of type Vector{Any} are not callable
Use square brackets for indexing an Array.
The object of type Vector{Any} exists, but no method is defined for this combination of argument types when trying to treat it as a callable object.
Stacktrace:
[1] plot_hits(times::Vector{Any}, hit_types::Vector{Any})
@ Main c:\Users\margo\JuliaRepo\j2\Implementierung\src\TimeGraph.jl:55
[2] top-level scope
@ c:\Users\margo\JuliaRepo\j2\Implementierung\src\TimeGraph.jl:63

2

Why don’t the stack trace’s line numbers match the code you shared? The code only has 56 lines, the stack trace starts at line 63. If we treat the plot_hits call on the last line as line 63 instead, then line 55 would be spec = ..., so data, mapping, visual are called, worth a type check.