# Error showing value of type SparseMatrixCSC
**URL:** https://discourse.julialang.org/t/error-showing-value-of-type-sparsematrixcsc/128857
**Category:** General Usage
**Tags:** question, sparsearrays
**Created:** [May 9, 2025, 12:50am UTC](https://discourse.julialang.org/t/error-showing-value-of-type-sparsematrixcsc/128857 "2025-05-09T00:50:14Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@WalterMadelim](https://discourse.julialang.org/u/WalterMadelim)
#### Post date: [May 9, 2025, 12:50am UTC](https://discourse.julialang.org/t/error-showing-value-of-type-sparsematrixcsc/128857/1 "2025-05-09T00:50:14Z")
It appears that there is a valid SparseMatrixCSC, but cannot be shown.
```julia
julia> using SparseArrays
julia> A = [rand(-9:9, 2) for i in 1:2, j in 1:2]
2×2 Matrix{Vector{Int64}}:
[-6, -1] [-7, -6]
[5, 5] [0, -1]
julia> S = sparse(A)
2×2 SparseMatrixCSC{Vector{Int64}, Int64} with 4 stored entries:
[-6, -1] [-7, -6]
[5, 5] [0, -1]
julia> I, J, V = findnz(S); pop!.([I, J, V]);
julia> @info "see" I J V
┌ Info: see
│ I =
│ 3-element Vector{Int64}:
│ 1
│ 2
│ 1
│ J =
│ 3-element Vector{Int64}:
│ 1
│ 1
│ 2
│ V =
│ 3-element Vector{Vector{Int64}}:
│ [-6, -1]
│ [5, 5]
└ [-7, -6]
julia> S_revised = sparse(I, J, V)
2×2 SparseMatrixCSC{Vector{Int64}, Int64} with 3 stored entries:
Error showing value of type SparseMatrixCSC{Vector{Int64}, Int64}:
SYSTEM (REPL): showing an error caused an error
ERROR: MethodError: no method matching zero(::Type{Vector{Int64}})
The function `zero` exists, but no method is defined for this combination of argument types.
Closest candidates are:
zero(::Type{Union{}}, Any...)
@ Base number.jl:310
zero(::Type{Missing})
@ Base missing.jl:104
zero(::Missing)
@ Base missing.jl:101
...
Stacktrace:
[1] print_response(errio::IO, response::Any, backend::Union{…}, show_value::Bool, have_color::Bool, specialdisplay::Union{…})
@ REPL C:\Users\34682\.julia\juliaup\julia-1.11.5+0.x64.w64.mingw32\share\julia\stdlib\v1.11\REPL\src\REPL.jl:446
[2] (::REPL.var"#70#71"{REPL.LineEditREPL, Pair{Any, Bool}, Bool, Bool})(io::Any)
@ REPL C:\Users\34682\.julia\juliaup\julia-1.11.5+0.x64.w64.mingw32\share\julia\stdlib\v1.11\REPL\src\REPL.jl:405
[3] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
@ REPL C:\Users\34682\.julia\juliaup\julia-1.11.5+0.x64.w64.mingw32\share\julia\stdlib\v1.11\REPL\src\REPL.jl:678
[4] print_response(repl::REPL.AbstractREPL, response::Any, show_value::Bool, have_color::Bool)
@ REPL C:\Users\34682\.julia\juliaup\julia-1.11.5+0.x64.w64.mingw32\share\julia\stdlib\v1.11\REPL\src\REPL.jl:403
[5] (::REPL.var"#do_respond#100"{Bool, Bool, REPL.var"#116#134"{…}, REPL.LineEditREPL, REPL.LineEdit.Prompt})(s::REPL.LineEdit.MIState, buf::Any, ok::Bool)
@ REPL C:\Users\34682\.julia\juliaup\julia-1.11.5+0.x64.w64.mingw32\share\julia\stdlib\v1.11\REPL\src\REPL.jl:1035
[6] #invokelatest#2
@ .\essentials.jl:1055 [inlined]
[7] invokelatest
@ .\essentials.jl:1052 [inlined]
[8] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
@ REPL.LineEdit C:\Users\34682\.julia\juliaup\julia-1.11.5+0.x64.w64.mingw32\share\julia\stdlib\v1.11\REPL\src\LineEdit.jl:2755
[9] run_frontend(repl::REPL.LineEditREPL, backend::REPL.REPLBackendRef)
@ REPL C:\Users\34682\.julia\juliaup\julia-1.11.5+0.x64.w64.mingw32\share\julia\stdlib\v1.11\REPL\src\REPL.jl:1506
[10] (::REPL.var"#79#85"{REPL.LineEditREPL, REPL.REPLBackendRef})()
@ REPL C:\Users\34682\.julia\juliaup\julia-1.11.5+0.x64.w64.mingw32\share\julia\stdlib\v1.11\REPL\src\REPL.jl:497
Some type information was truncated. Use `show(err)` to see complete types.
```
---
### Author:  [@danielwe](https://discourse.julialang.org/u/danielwe)
#### Post date: [May 9, 2025, 1:19am UTC](https://discourse.julialang.org/t/error-showing-value-of-type-sparsematrixcsc/128857/2 "2025-05-09T01:19:08Z")
Long story short: the concept of a sparse matrix only makes sense when the element type has a uniquely defined zero. `Vector{Int}` doesn’t have this because it doesn’t encode the length of the vector in the type. If you want a sparse array where the elements are vectors of a particular length, you should use StaticArrays.jl, which does encode the length in the type. Here’s what your example would look like:
```julia-repl
julia> using SparseArrays, StaticArrays
julia> A = [@SVector rand(-9:9, 2) for i in 1:2, j in 1:2]
2×2 Matrix{SVector{2, Int64}}:
[-1, -1] [-7, -2]
[-4, 8] [-8, 3]
julia> S = sparse(A)
2×2 SparseMatrixCSC{SVector{2, Int64}, Int64} with 4 stored entries:
[-1, -1] [-7, -2]
[-4, 8] [-8, 3]
julia> I, J, V = findnz(S); pop!.([I, J, V]);
julia> sparse(I, J, V)
2×2 SparseMatrixCSC{SVector{2, Int64}, Int64} with 3 stored entries:
[-1, -1] [-7, -2]
[-4, 8] ⋅
```
* * *
Longer explanation: This is more fundamental than a display problem. It’s a problem determining what the value of a structural zero should be in this matrix.
```julia-repl
julia> using SparseArrays
julia> A = [rand(-9:9, 2) for i in 1:2, j in 1:2]
2×2 Matrix{Vector{Int64}}:
[1, -9] [6, -8]
[5, 6] [-3, 4]
julia> S = sparse(A)
2×2 SparseMatrixCSC{Vector{Int64}, Int64} with 4 stored entries:
[1, -9] [6, -8]
[5, 6] [-3, 4]
julia> I, J, V = findnz(S); pop!.([I, J, V]);
julia> S2 = sparse(I, J, V);
julia> S2[2, 2]
ERROR: MethodError: no method matching zero(::Type{Vector{Int64}})
[...]
```
I assume you want `S2[2, 2] == [0, 0]`, but the problem is that the lengths of vectors aren’t encoded in their type, so there’s no way to know that you want `[0, 0]` and not `[0]` or `[0, 0, 0, 0, 0, 0]`.
For a starker illustration of the problem, consider the following: what should `S2[2, 2]` return here?
```julia-repl
julia> M = Matrix{Vector{Int64}}(undef, 2, 2);
julia> for i in 1:4
M[i] = [i for _ in 1:i]
end
julia> S = sparse(M)
2×2 SparseMatrixCSC{Vector{Int64}, Int64} with 4 stored entries:
[1] [3, 3, 3]
[2, 2] [4, 4, 4, 4]
julia> I, J, V = findnz(S); pop!.([I, J, V]);
julia> S2 = sparse(I, J, V);
julia> S2[2, 2]
ERROR: MethodError: no method matching zero(::Type{Vector{Int64}})
[...]
```
---
### Author:  [@danielwe](https://discourse.julialang.org/u/danielwe)
#### Post date: [May 9, 2025, 1:56am UTC](https://discourse.julialang.org/t/error-showing-value-of-type-sparsematrixcsc/128857/3 "2025-05-09T01:56:06Z")
Found a relevant issue and offered my perspective (which is that this should error on construction since the arrays are unusable anyway): [Sparse array of string types · Issue #512 · JuliaSparse/SparseArrays.jl · GitHub](https://github.com/JuliaSparse/SparseArrays.jl/issues/512)