How to unpack multidimensional array into variables in Julia

Question

In Python I can do:

a = array([[1,2],[3,4]])
row1, row2 = a

Is there an equivalent one-liner in Julia? This doesn't seem to work:

a = [[1 2]; [3 4]]
row1, row2 = a

Instead it sets row1=1 and row2=3. Thanks!

Answer 1

Depending on what you are doing you could use a Vector{Vector{T}}, like python list of lists instead of a Matrix (Array{T,2}).

In v0.5+ it just works, with [ , ]:

julia> VERSION
v"0.5.0-dev+4440"

julia> a = [[1, 2], [3, 4]]
2-element Array{Array{Int64,1},1}:
 [1, 2]
 [3, 4]

julia> a = [[1, 2]; [3, 4]]
4-element Array{Int64,1}:
 1
 2
 3
 4

julia> row1, row2 = a;

julia> (row1, row2)
(2-element Array{Int64,1}:
 1
 2,2-element Array{Int64,1}:
 3
 4)

In v0.4+ you need to type the array as an array of arrays, like so:

julia> VERSION
v"0.4.5"

julia> a = Vector[[1, 2], [3, 4]]
2-element Array{Array{T,1},1}:
 [1,2]
 [3,4]

julia> b = [[1, 2]; [3, 4]]
4-element Array{Int64,1}:
 1
 2
 3
 4

julia> c = [[1, 2], [3, 4]]
WARNING: [a,b] concatenation is deprecated; use [a;b] instead
 in depwarn at deprecated.jl:73
 in oldstyle_vcat_warning at abstractarray.jl:29
 in vect at abstractarray.jl:32
while loading no file, in expression starting on line 0
4-element Array{Int64,1}:
 1
 2
 3
 4

julia> row1, row2 = a;

julia> row1, row2
([1,2],[3,4])