How do I add a dimension to an array? (opposite of `squeeze`)

Question

I can never remember how to do this this.

How can go

• from a Vector (size (n1)) to a Column Matrix (size (n1,1))?
• or from a Matrix (size (n1,n2)) to a Array{T,3} (size (n1,n2,1))?
• or from a Array{T,3} (size (n1,n2,n3)) to a Array{T,4} (size (n1,n2,n3, 1))?
• and so forth.

I want to know to take Array and use it to define a new Array with an extra singleton trailing dimension. I.e. the opposite of squeeze

Answer 1

Try this

function extend_dims(A,which_dim)
       s = [size(A)...]
       insert!(s,which_dim,1)
       return reshape(A, s...)
       end

the variable extend_dim specifies which dimension to extend

Thus

extend_dims(randn(3,3),1)

will produce a 1 x 3 x 3 array and so on.

I find this utility helpful when passing data into convolutional neural networks.