# Vector of tuples vs Matrix type

**URL:** <https://discourse.julialang.org/t/vector-of-tuples-vs-matrix-type/48484>\
**Category:** New to Julia\
**Created:** [October 16, 2020, 11:13am UTC](https://discourse.julialang.org/t/vector-of-tuples-vs-matrix-type/48484 "2020-10-16T11:13:09Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![bcsj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bcsj/32/18526_2.png) [@bcsj](https://discourse.julialang.org/u/bcsj)\
**Post date:** [October 16, 2020, 11:13am UTC](https://discourse.julialang.org/t/vector-of-tuples-vs-matrix-type/48484/1 "2020-10-16T11:13:09Z")

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I’m pretty new to Julia and was wondering what the preferred practice for storing something like a bunch of coordinates, mesh triangles or graph edges?

Say I want to store edges in a graph. The vertices are labelled by indices 1,2,3,…  
Would I want to be storing the edges as 2-tuples in a Vector{Tuple{Int, Int}}, since I know that each edge is stored as exactly 2 vertex indices?  
Or would it be better to store the edges in a 2-by-N matrix structure Matrix{Int} (each edge stored as a column, since afaik looping over columns is preferred over rows)?  
Or is there a third way I don’t know of which is better than both of the above?

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**Author:** ![mcabbott](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mcabbott/32/6603_2.png) [@mcabbott](https://discourse.julialang.org/u/mcabbott)\
**Post date:** [October 16, 2020, 11:38am UTC](https://discourse.julialang.org/t/vector-of-tuples-vs-matrix-type/48484/2 "2020-10-16T11:38:32Z")

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These in fact have the same storage, so you can use either and convert for free. A third option would be StaticArrays, which are essentially tuples wrapped up to look like vectors:

```julia
julia> mat = rand(1:99, 2,3)
2×3 Matrix{Int64}:
 19 7 4
  9 11 52

julia> reinterpret(reshape, Tuple{Int,Int}, mat) # with Julia 1.6, or Compat.jl
3-element reinterpret(reshape, Tuple{Int64, Int64}, ::Matrix{Int64}) with eltype Tuple{Int64, Int64}:
 (19, 9)
 (7, 11)
 (4, 52)

julia> using StaticArrays

julia> svecs = [SVector(rand(1:99), rand(1:99)) for _ in 1:3]
3-element Vector{SVector{2, Int64}}:
 [7, 17]
 [11, 36]
 [69, 80]

julia> reshape(reinterpret(Int, svecs),2,:) # works on Julia <= 1.5 too
2×3 reshape(reinterpret(Int64, ::Vector{SVector{2, Int64}}), 2, 3) with eltype Int64:
  7 11 69
 17 36 80

```

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**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [October 16, 2020, 12:03pm UTC](https://discourse.julialang.org/t/vector-of-tuples-vs-matrix-type/48484/3 "2020-10-16T12:03:21Z")

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What the best solution is, depends on what you want to do. If you intend to do a lot of operations on the 2-vectors, then a vector of StaticVectors could be very advantageous. If you are doing ordinary matrix operations, then a matrix is probably better.

In addition to what @mcabbott suggested, you have a fourth option: [https://github.com/mateuszbaran/HybridArrays.jl](https://github.com/mateuszbaran/HybridArrays.jl) which try to combine the advantages of both approaches. I haven’t tried it, though.