We know that the notation [1, 2, 3] is used to create an array. In fact, this notation denotes a special type of array, called a (column) vector in Julia, as shown in the following screenshot:

To create this as a row vector (1 2 3), use the notation [1 2 3] with spaces instead of commas. This array is of type 1 x 3 Array{Int64,2}, so it has two dimensions. (The spaces used in [1, 2, 3] are for readability only, we could have written this as [1,2,3]).

A matrix is a two- or multi-dimensional array (in fact, a matrix is an alias for the two-dimensional case). In fact, we can write this as follows:

Array{Int64, 1} == Vector{Int64} #> true
Array{Int64, 2} == Matrix{Int64} #> true

As matrices are so prevalent in data science and numerical programming, Julia has an amazing range of functionalities for them.

To create a matrix, use space-separated values for the columns and semicolon-separated for the rows:

// code in Chapter 5\matrices.jl:
matrix = [1 2; 3 4] 
    2x2 Array{Int64,2...