CODEWITHSUNDEEP
julia
Abhijith
Abhijith

Reputation: 1208

Concatenating arrays in Julia

If the two Int arrays are, a = [1;2;3] and b = [4;5;6], how do we concatenate the two arrays in both the dimensions? The expected outputs are, 

julia> out1
6-element Array{Int64,1}:
 1
 2
 3
 4
 5
 6

julia> out2
3x2 Array{Int64,2}:
 1  4
 2  5
 3  6

Upvotes: 51

Views: 80797

Answers (5)

Kadir Gunel
Kadir Gunel

Reputation: 331

Functional way to concatanate 2 arrays is to use reduce function.

a = rand(10, 1)
b = rand(10, 1)
c = reduce(hcat, [a, b])

Upvotes: 2

Jason D
Jason D

Reputation: 303

when encountered Array{Array,1}, the grammer is a little bit different, like this:

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

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

julia> hcat(a)
2×1 Array{Array{Int64,1},2}:
 [1, 2]
 [3, 4]

julia> vcat(a...)
4-element Array{Int64,1}:
 1
 2
 3
 4

julia> hcat(a...)
2×2 Array{Int64,2}:
 1  3
 2  4

ref:

... combines many arguments into one argument in function definitions In the context of function definitions, the ... operator is used to combine many different arguments into a single argument. This use of ... for combining many different arguments into a single argument is called slurping

Upvotes: 2

Landon
Landon

Reputation: 828

You can use the cat function to concatenate any number of arrays along any dimension. The first input is the dimension over which to perform the concatenation; the remaining inputs are all of the arrays you wish to concatenate together

a = [1;2;3]
b = [4;5;6]

## Concatenate 2 arrays along the first dimension
cat(1,a,b)
6-element Array{Int64,1}:
 1
 2
 3
 4
 5
 6

## Concatenate 2 arrays along the second dimension
cat(2,a,b)
3x2 Array{Int64,2}:
 1  4
 2  5
 3  6

## Concatenate 2 arrays along the third dimension
cat(3,a,b)
3x1x2 Array{Int64,3}:
[:, :, 1] =
 1
 2
 3

[:, :, 2] =
 4
 5
 6

Upvotes: 17

user6847814
user6847814

Reputation: 456

Square brackets can be used for concatenation:

julia> a, b = [1;2;3], [4;5;6]
([1,2,3],[4,5,6])

julia> [a; b]
6-element Array{Int64,1}:
 1
 2
 3
 4
 5
 6

julia> [a b]
3×2 Array{Int64,2}:
 1  4
 2  5
 3  6

Upvotes: 34

HarmonicaMuse
HarmonicaMuse

Reputation: 7893

Use the vcat and hcat functions:

julia> a, b = [1;2;3], [4;5;6]
([1,2,3],[4,5,6])

help?> vcat
Base.vcat(A...)

   Concatenate along dimension 1

julia> vcat(a, b)
6-element Array{Int64,1}:
 1
 2
 3
 4
 5
 6

help?> hcat
Base.hcat(A...)

   Concatenate along dimension 2

julia> hcat(a, b)
3x2 Array{Int64,2}:
 1  4
 2  5
 3  6

Upvotes: 49

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