Error trying to `show` KeyedArray with undef values

I ran into this when using wrapdims on a DataFrame which had a column containing vectors, leading wrapdims (which calls similar) to produce a KeyedArray with #undef values

Is wrapdims produce #undef values itself a bug or is that expected behaviour? I suppose expected behaviour and the default=... keyword must be used to avoid it?

Anyway, here's the error:

julia> df = DataFrame(r=1:100, c=1:100, v=fill([1], 100));

julia> AxisKeys.wrapdims(df, :v, :r, :c)
2-dimensional KeyedArray(NamedDimsArray(...)) with keys:
↓   r ∈ 100-element Vector{Int64}
→   c ∈ 100-element Vector{Int64}
And data, 100×100 Matrix{Vector{Int64}}:
Error showing value of type KeyedArray{Vector{Int64}, 2, NamedDimsArray{(:r, :c), Vector{Int64}, 2, Matrix{Vector{Int64}}}, Tuple{Vector{Int64}, Vector{Int64}}}:
ERROR: UndefRefError: access to undefined reference
Stacktrace:
  [1] getindex
    @ ./array.jl:925 [inlined]
  [2] macro expansion
    @ ./multidimensional.jl:903 [inlined]
  [3] macro expansion
    @ ./cartesian.jl:64 [inlined]
  [4] _unsafe_getindex!
    @ ./multidimensional.jl:898 [inlined]
  [5] _unsafe_getindex(::IndexLinear, ::Matrix{Vector{Int64}}, ::UnitRange{Int64}, ::UnitRange{Int64})
    @ Base ./multidimensional.jl:889
  [6] _getindex
    @ ./multidimensional.jl:875 [inlined]
  [7] getindex
    @ ./abstractarray.jl:1236 [inlined]
  [8] keyed_print_matrix(io::IOContext{Base.TTY}, A::KeyedArray{Vector{Int64}, 2, NamedDimsArray{(:r, :c), Vector{Int64}, 2, Matrix{Vector{Int64}}}, Tuple{Vector{Int64}, Vector{Int64}}}, reduce_size::Bool)
    @ AxisKeys ~/.julia/packages/AxisKeys/MK99E/src/show.jl:101
  [9] print_matrix
    @ ~/.julia/packages/AxisKeys/MK99E/src/show.jl:77 [inlined]
 [10] print_array
    @ ./arrayshow.jl:358 [inlined]
 [11] show(io::IOContext{Base.TTY}, #unused#::MIME{Symbol("text/plain")}, X::KeyedArray{Vector{Int64}, 2, NamedDimsArray{(:r, :c), Vector{Int64}, 2, Matrix{Vector{Int64}}}, Tuple{Vector{Int64}, Vector{Int64}}})
    @ Base ./arrayshow.jl:399
 [12] (::REPL.var"#43#44"{REPL.REPLDisplay{REPL.LineEditREPL}, MIME{Symbol("text/plain")}, Base.RefValue{Any}})(io::Any)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:267
 [13] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:521
 [14] display(d::REPL.REPLDisplay, mime::MIME{Symbol("text/plain")}, x::Any)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:260
 [15] display(d::REPL.REPLDisplay, x::Any)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:272
 [16] display(x::Any)
    @ Base.Multimedia ./multimedia.jl:328
 [17] #invokelatest#2
    @ ./essentials.jl:729 [inlined]
 [18] invokelatest
    @ ./essentials.jl:726 [inlined]
 [19] print_response(errio::IO, response::Any, show_value::Bool, have_color::Bool, specialdisplay::Union{Nothing, AbstractDisplay})
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:296
 [20] (::REPL.var"#45#46"{REPL.LineEditREPL, Pair{Any, Bool}, Bool, Bool})(io::Any)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:278
 [21] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:521
 [22] print_response(repl::REPL.AbstractREPL, response::Any, show_value::Bool, have_color::Bool)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:276
 [23] (::REPL.var"#do_respond#66"{Bool, Bool, REPL.var"#77#87"{REPL.LineEditREPL, REPL.REPLHistoryProvider}, REPL.LineEditREPL, REPL.LineEdit.Prompt})(s::REPL.LineEdit.MIState, buf::Any, ok::Bool)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:857
 [24] #invokelatest#2
    @ ./essentials.jl:729 [inlined]
 [25] invokelatest
    @ ./essentials.jl:726 [inlined]
 [26] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
    @ REPL.LineEdit /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/LineEdit.jl:2510
 [27] run_frontend(repl::REPL.LineEditREPL, backend::REPL.REPLBackendRef)
    @ REPL /Applications/Julia-1.8.app/Contents/Resources/julia/share/julia/stdlib/v1.8/REPL/src/REPL.jl:1248
 [28] (::REPL.var"#49#54"{REPL.LineEditREPL, REPL.REPLBackendRef})()
    @ REPL ./task.jl:484

The error seems to be triggered only by the plain-text show:

julia> arr = similar(KeyedArray(fill([1], 2, 3); a=1:2, b=1:3));

julia> show(stdout, arr)
[#undef #undef #undef; #undef #undef #undef]
julia> show(stdout, MIME("text/plain"), arr)
2-dimensional KeyedArray(NamedDimsArray(...)) with keys:
↓   a ∈ 2-element UnitRange{Int64}
→   b ∈ 3-element UnitRange{Int64}
And data, 2×3 Matrix{Vector{Int64}}:
ERROR: UndefRefError: access to undefined reference
Stacktrace:
  [1] getindex
    @ ./array.jl:925 [inlined]
  [2] macro expansion
    @ ./multidimensional.jl:903 [inlined]
  [3] macro expansion
    @ ./cartesian.jl:64 [inlined]
  [4] _unsafe_getindex!
    @ ./multidimensional.jl:898 [inlined]
  [5] _unsafe_getindex(::IndexLinear, ::Matrix{Vector{Int64}}, ::Base.Slice{Base.OneTo{Int64}}, ::Base.Slice{Base.OneTo{Int64}})
    @ Base ./multidimensional.jl:889
  [6] _getindex
    @ ./multidimensional.jl:875 [inlined]
  [7] getindex
    @ ./abstractarray.jl:1236 [inlined]
  [8] keyed_print_matrix(io::IOContext{Base.TTY}, A::KeyedArray{Vector{Int64}, 2, NamedDimsArray{(:a, :b), Vector{Int64}, 2, Matrix{Vector{Int64}}}, Tuple{UnitRange{Int64}, UnitRange{Int64}}}, reduce_size::Bool)
    @ AxisKeys ~/.julia/packages/AxisKeys/MK99E/src/show.jl:101
  [9] print_matrix
    @ ~/.julia/packages/AxisKeys/MK99E/src/show.jl:77 [inlined]
 [10] print_array
    @ ./arrayshow.jl:358 [inlined]
 [11] show(io::Base.TTY, #unused#::MIME{Symbol("text/plain")}, X::KeyedArray{Vector{Int64}, 2, NamedDimsArray{(:a, :b), Vector{Int64}, 2, Matrix{Vector{Int64}}}, Tuple{UnitRange{Int64}, UnitRange{Int64}}})
    @ Base ./arrayshow.jl:399
 [12] top-level scope
    @ REPL[64]:1

by the look of it, due to keyed_print_matrix not checking isassigned?

Reproduce the issue with the similar(KeyedArray(...)) example and compare plain show with MIME("text/plain"). Inspect show.jl, especially keyed_print_matrix around line 101, where the stack trace points. Done means displaying a KeyedArray containing unassigned values no longer raises UndefRefError.