Note: This question/answer is copied from the Julia Slack channel.
If I have an arbitrary Julia Array, how can I add another dimension.
julia> a = [1, 2, 3, 4]
4-element Array{Int64,1}:
1
2
3
4
The desired output would be e.g.:
julia> a[some_magic, :]
1×4 Array{Int64,2}:
1 2 3 4
Or:
julia> a[:, some_magic]
4×1 Array{Int64,2}:
1
2
3
4
A less tricky thing I usually do to achieve this is:
julia> reshape(a, 1, :)
1×4 Array{Int64,2}:
1 2 3 4
julia> reshape(a, :, 1)
4×1 Array{Int64,2}:
1
2
3
4
(it also seems to involve less typing)
Finally a common case requiring transforming a vector to a column matrix can be done:
julia> hcat(a)
4×1 Array{Int64,2}:
1
2
3
4
EDIT also if you add trailing dimensions you can simply use ::
julia> a = [1,2,3,4]
4-element Array{Int64,1}:
1
2
3
4
julia> a[:,:]
4×1 Array{Int64,2}:
1
2
3
4
julia> a[:,:,:]
4×1×1 Array{Int64,3}:
[:, :, 1] =
1
2
3
4
The trick is so use [CartesianIndex()] to create the additional axes:
julia> a[[CartesianIndex()], :]
1×4 Array{Int64,2}:
1 2 3 4
And:
julia> a[:, [CartesianIndex()]]
4×1 Array{Int64,2}:
1
2
3
4
If you want to get closer to numpy's syntax, you can define:
const newaxis = [CartesianIndex()]
And just use newaxis.