DimensionMismatch error with an animation for the size changing array with Observable

[michikazjp]

I am trying to make an animation with size changing array with Observable like

using GLMakie
function plot_graph_realtime(x)
    fig=Figure()
    ax=Axis(fig[1,1])
    it=Observable(1)
    @lift(lines!(ax,x[1,1:$it],x[2,1:$it]))
    xlims!(ax,-1,3)
    ylims!(ax,-1,3)
    display(fig)
    for i=1:size(x,2)
        sleep(1)
        it[]=i
    end
end
plot_graph_realtime([0 1 2 3;0 1 2 3])

The above code does work. But the similar code like

using GLMakie
function plot_graph_realtime(x)
    fig=Figure()
    ax=Axis(fig[1,1])
    it=Observable(1)
    lines!(ax,@lift(x[1,1:$it]),@lift(x[2,1:$it]))
    xlims!(ax,-1,3)
    ylims!(ax,-1,3)
    display(fig)
    for i=1:size(x,2)
        sleep(1)
        it[]=i
    end
end
plot_graph_realtime([0 1 2 3;0 1 2 3])

does not work with the following error

DimensionMismatch("arrays could not be broadcast to a common size; got a dimension with lengths 3 and 2")

Stacktrace:
  [1] _bcs1
    @ ./broadcast.jl:516 [inlined]
  [2] _bcs
    @ ./broadcast.jl:510 [inlined]
  [3] broadcast_shape
    @ ./broadcast.jl:504 [inlined]
  [4] combine_axes
    @ ./broadcast.jl:499 [inlined]
  [5] instantiate
    @ ./broadcast.jl:281 [inlined]
  [6] materialize
    @ ./broadcast.jl:860 [inlined]
  [7] convert_arguments(P::PointBased, x::Vector{Int64}, y::Vector{Int64})
    @ Makie ~/.julia/packages/Makie/Ppzqh/src/conversions.jl:136
  [8] convert_arguments(::Type{Lines{Tuple{Vector{Int64}, Vector{Int64}}}}, ::Vector{Int64}, ::Vararg{Vector{Int64}}; kw::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ Makie ~/.julia/packages/Makie/Ppzqh/src/conversions.jl:10
  [9] convert_arguments(::Type{Lines{Tuple{Vector{Int64}, Vector{Int64}}}}, ::Vector{Int64}, ::Vector{Int64})
    @ Makie ~/.julia/packages/Makie/Ppzqh/src/conversions.jl:8
 [10] (::Makie.var"#142#144"{Attributes, Observable{Tuple{Vector{Point{2, Float32}}}}, DataType})(kwargs::Tuple{}, args::Tuple{Vector{Int64}, Vector{Int64}})
    @ Makie ~/.julia/packages/Makie/Ppzqh/src/interfaces.jl:326
 [11] (::Observables.var"#callback#13"{Makie.var"#142#144"{Attributes, Observable{Tuple{Vector{Point{2, Float32}}}}, DataType}, Tuple{Observable{Tuple{}}, Observable{Tuple{Vector{Int64}, Vector{Int64}}}}})(x::Any)
    @ Observables ~/.julia/packages/Observables/ynr7h/src/Observables.jl:339
 [12] #invokelatest#2
    @ ./essentials.jl:716 [inlined]
 [13] invokelatest
    @ ./essentials.jl:714 [inlined]
 [14] notify
    @ ~/.julia/packages/Observables/ynr7h/src/Observables.jl:143 [inlined]
 [15] setindex!(observable::Observable, val::Any)
    @ Observables ~/.julia/packages/Observables/ynr7h/src/Observables.jl:86
 [16] #15
    @ ~/.julia/packages/Observables/ynr7h/src/Observables.jl:393 [inlined]
 [17] (::Observables.var"#callback#13"{Observables.var"#15#16"{typeof(tuple), Observable{Tuple{Vector{Int64}, Vector{Int64}}}}, Tuple{Observable{Vector{Int64}}, Observable{Vector{Int64}}}})(x::Any)
    @ Observables ~/.julia/packages/Observables/ynr7h/src/Observables.jl:339
 [18] #invokelatest#2
    @ ./essentials.jl:716 [inlined]
 [19] invokelatest
    @ ./essentials.jl:714 [inlined]
 [20] notify
    @ ~/.julia/packages/Observables/ynr7h/src/Observables.jl:143 [inlined]
 [21] setindex!(observable::Observable, val::Any)
    @ Observables ~/.julia/packages/Observables/ynr7h/src/Observables.jl:86
 [22] #15
    @ ~/.julia/packages/Observables/ynr7h/src/Observables.jl:393 [inlined]
 [23] (::Observables.var"#callback#13"{Observables.var"#15#16"{var"#499#501"{Matrix{Int64}}, Observable{Vector{Int64}}}, Tuple{Observable{Int64}}})(x::Any)
    @ Observables ~/.julia/packages/Observables/ynr7h/src/Observables.jl:339
 [24] #invokelatest#2
    @ ./essentials.jl:716 [inlined]
 [25] invokelatest
    @ ./essentials.jl:714 [inlined]
 [26] notify
    @ ~/.julia/packages/Observables/ynr7h/src/Observables.jl:143 [inlined]
 [27] setindex!
    @ ~/.julia/packages/Observables/ynr7h/src/Observables.jl:86 [inlined]
 [28] plot_graph_realtime(x::Matrix{Int64})
    @ Main ./In[135]:12
 [29] top-level scope
    @ In[135]:15
 [30] eval
    @ ./boot.jl:373 [inlined]
 [31] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
    @ Base ./loading.jl:1196

Do you have any idea for the reason with the error?

[fatteneder]

In your first example, you create one Observable which wraps a call to lines! with two arrays that area always of equal length.
In your second example, you create two Observables and pass them to a lines! call.
When you then trigger an update with it[]=i the two Observables are updated separately one after the other. This causes lines! to fail, because it sees two arrays with different lengths for a short time.

If you want to use two Observables then you should update one 'silently' (e.g. without sending notifications to its listeners) and trigger a replot with the second, e.g.

using GLMakie
function plot_graph_realtime(x)
    fig=Figure()
    ax=Axis(fig[1,1])
    it=Observable(1)
    obs_x1 = Observable(x[1,1:it[]])
    obs_x2 = Observable(x[2,1:it[]])
    on(it) do _it
       # using .val to change the value will not propagate an update
       obs_x1.val = x[1,1:_it]
       # using [] will trigger an update
       obs_x2[] = x[2,1:_it]
    end
    lines!(ax,obs_x1, obs_x2)
    xlims!(ax,-1,3)
    ylims!(ax,-1,3)
    display(fig)
    for i=1:size(x,2)
        sleep(1)
        it[]=i
    end
end
plot_graph_realtime([0 1 2 3;0 1 2 3])

[michikazjp]

Thanks a lot!
Probably,
obs_x2[] = x[2:1:_it]
in line 12 should be corrected to be
obs_x2[] = x[2,1:_it]
Anyway, your suggestion worked in better than my first code.

[likev]

see also #3658