Julia array tips - Julia Tips

Convert a vector of vectors to a matrix¶

Use the stack function.

stack([[1,0,1],[0,0,1]], dims=1) == [ 1 0 1 ; 0 0 1 ]

true

If you only need broadcast operations, RecursiveArrayTools.jl wraps a vector of vectors.

using RecursiveArrayTools

a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
b = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
vA = VectorOfArray(a)
vB = VectorOfArray(b)

vA .* vB

VectorOfArray{Int64,2}:
3-element Vector{Vector{Int64}}:
 [1, 4, 9]
 [16, 25, 36]
 [49, 64, 81]

Convert a VectorOfArray into a matrix.

Matrix(vA .* vB)

3×3 Matrix{Int64}:
 1  16  49
 4  25  64
 9  36  81

Convert a linear index to 2D indices¶

Use CartesianIndices((nrow, ncol)): See https://discourse.julialang.org/t/julia-usage-how-to-get-2d-indexes-from-1d-index-when-accessing-a-2d-array/61440

x = rand((7, 10))
CI = CartesianIndices((7, 10))
for i in 1:length(x)
    r = CI[i][1]
    c = CI[i][2]
    @assert x[i] == x[r, c]
end

This notebook was generated using Literate.jl.