Multi-dimensional arrays
Intermediate Julia
Anthony Markham
Quantitative Developer
1D array recap
- A vector is simply an array with only one dimension.
# Create a 1-D array (vector)
my_1d_array = [1, 2, 3, 4, 5, 6]
6-element Vector{Int64}:
1
2
3
4
5
6
2D array structure
- A 2D array is also referred to as a matrix.
- A tabular representation of data, with multiple rows and columns.
- Remove the commas between elements, use the semicolon
;to denote a new row.
# Define a matrix
my_matrix = [1 2 3; 4 5 6]
2×3 Matrix{Int64}:
1 2 3
4 5 6
Indexing a 2D array
- Indexing is similar to vectors, but we need two indexes, not one.
- The first index is the row, and the second is the column.
2×3 Matrix{Int64}:
1 2 3
4 5 6
# Return '2' - first row, second column
println(my_matrix[1, 2])
2
Slicing a 2D array
- The colon
:operator allows us to select all values in a row or column. - This is the same as the previous DataFrame slicing that we have seen!
2×3 Matrix{Int64}:
1 2 3
4 5 6
# Return the entire third column
println(my_matrix[:, 3])
[3, 6]
getindex()
getindex()is another way to access elements within an array.- Pass the variable name and the two indices to return the value at these indices.
2×3 Matrix{Int64}:
1 2 3
4 5 6
println(getindex(stock, 1, 2))
2
2D array concatenation
- Array concatenation involves combining two arrays together by stacking them.
array_1 = [1 2 3; 4 5 6]
array_2 = [7 8 9; 10 11 12]
concat_array = [array_1; array_2]
4×3 Matrix{Int64}:
1 2 3
4 5 6
7 8 9
10 11 12
Let's practice!
Intermediate Julia
