What's the most efficient way to convert a Matrix{T} of size 1*N or N*1 in Julia to a Vector{T}?

Question

What's the most efficient way to convert a Matrix{T} of size 1*N or N*1 in Julia to a Vector{T}?

For example, say I have

a = [1,3,5] b = a' 

Both a and b are of type Array{Int,2} (i.e. Matrix{Int}). What are the most efficient ways to convert a and b to type Array{Int,1} (i.e. Vector{Int})?

One approach is:

a_vec = [x::Int for x in a] b_vec = [x::Int for x in b] 

Answer 1

You can use the vec() function. It's faster than the list comprehension and scales better with number of elements ;) For a matrix of 1000x1:

julia> const a = reshape([1:1000],1000,1);  julia> typeof(a) Array{Int64,2}  julia> vec_a = [x::Int for x in a];  julia> typeof(vec_a) Array{Int64,1}  julia> vec_aII = vec(a);  julia> typeof(vec_aII) Array{Int64,1} 

6.41e-6 seconds # list comprehension

2.92e-7 seconds # vec()

Answer 2

I would tend to use squeeze to do this if the matrix is 1xN or Nx1:

squeeze(ones(3, 1)) squeeze(ones(1, 3)) 

Not sure if that's more efficient than using vec or reshape.