# Methods for vectors of sparse vs dense matrices
**URL:** https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404
**Category:** General Usage
**Tags:** function, vector, sparse, matrices
**Created:** [May 18, 2021, 11:03pm UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404 "2021-05-18T23:03:33Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@gvdr](https://discourse.julialang.org/u/gvdr)
#### Post date: [May 18, 2021, 11:03pm UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404/1 "2021-05-18T23:03:34Z")
I’m writing a function which should have two methods, one for vectors of sparse matrices (`SparseMatrixCSC`) and one for vectors of dense matrices.
I don’t want to pre/dicate about the nature of those matrices beyond the point of distinguishing between sparse and dense. So far, my definition look like:
```julia
function f(Tₜ::T) where T <: Vector{SparseMatrixCSC{Float64, Int64}}.
```
and
```julia
function f(Tₜ::T) where T <: Vector{Matrix{Float64}}.
```
yet I want to get rid of that `{Float64}` specification.
How would I do it?
Eventually, I would like to write the method so that it would apply to _any_ `SparseMatrixCSC` or to any `Matrix` (but distinguishing them).
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [May 18, 2021, 11:07pm UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404/2 "2021-05-18T23:07:32Z")
Does it work if you just remove the element type? Like
```julia
Vector{Matrix}
```
or
```julia
Vector{<:Matrix}
```
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [May 18, 2021, 11:09pm UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404/3 "2021-05-18T23:09:14Z")
> [@gvdr](#):
>
> `function f(Tₜi::T) <: where T <: Vector{SparseMatrixCSC{Float64, Int64}}.`
I would do something more abstract, like:
```julia
f(Tₜ::AbstractVector{<:AbstractSparseMatrix}) = ...
f(Tₜ::AbstractVector{<:AbstractMatrix}) = ...
```
---
### Author:  [@gvdr](https://discourse.julialang.org/u/gvdr)
#### Post date: [May 18, 2021, 11:11pm UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404/4 "2021-05-18T23:11:10Z")
The first does not work (that was my initial guess), but the second does!
I didn’t know you could use a nested inherit type in that way, nice!
---
### Author:  [@gvdr](https://discourse.julialang.org/u/gvdr)
#### Post date: [May 18, 2021, 11:12pm UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404/5 "2021-05-18T23:12:26Z")
Thanks! This is perfect 🙂
---
### Author:  [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)
#### Post date: [May 18, 2021, 11:12pm UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404/6 "2021-05-18T23:12:34Z")
```julia
function f(v::T) where T <: Vector{Matrix{N}} where N v[1]; end
f (generic function with 1 method)
julia> v1 = [rand(2,3)]
1-element Vector{Matrix{Float64}}:
[0.6498353443464961 0.8556641584648517 0.05535954378049679; 0.39224917246518864 0.35720373820135043 0.23334843425685636]
julia> f(v1)
2×3 Matrix{Float64}:
0.649835 0.855664 0.0553595
0.392249 0.357204 0.233348
julia>
```
Will that do?
---
### Author:  [@Seif\_Shebl](https://discourse.julialang.org/u/Seif_Shebl)
#### Post date: [May 19, 2021, 1:23am UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404/7 "2021-05-19T01:23:51Z")
> [@stevengj](#):
>
> ```julia
> f(Tₜ::AbstractVector{<:AbstractSparseMatrix}) = ...
> f(Tₜ::AbstractVector{<:AbstractMatrix}) = ...
>
> ```
I like @stevengj’s answer and I think it could still be made slightly shorter.
```julia
f(Tₜ::Vector{<:AbstractSparseMatrix}) = ...
f(Tₜ::Vector{<:AbstractMatrix}) = ...
```
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [May 19, 2021, 3:02am UTC](https://discourse.julialang.org/t/methods-for-vectors-of-sparse-vs-dense-matrices/61404/8 "2021-05-19T03:02:07Z")
> [@Seif\_Shebl](#):
>
> I like @stevengj’s answer and I think it could still be made slightly shorter.
>
> ```julia
> f(Tₜ::Vector{<:AbstractSparseMatrix}) = ...
> f(Tₜ::Vector{<:AbstractMatrix}) = ...
>
> ```
That’s less generic. Your way only allows the outer container to be Julia’s built-in `Vector` type, as opposed to some other `AbstractVector` container (e.g. an `OffsetArray`, an `AxisArrays`, etcetera).