Multi-dimensional Typed Arrays

Part of the Introduction To Luau section of Coddy's Lua journey. Lesson 19 of 73.

Grids, boards and matrices are arrays of arrays, and the type follows the same nesting: {{number}} is an array whose elements are {number} arrays.

local grid: {{number}} = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9},
}

local board: {{string}} = {
    {"white", "black"},
    {"black", "white"},
}

Nested indexing reads one level at a time: grid[2] is the second row (a {number}), and grid[2][1] is that row's first element: 4. Both indices are 1-based, so the top-left corner is grid[1][1], not grid[0][0].

Watch out when a row might not exist: grid[10] is nil, so grid[10][1] raises a runtime error: you'd be indexing into nil.

You can also build grids with loops: create an empty row, fill it with table.insert, then insert the whole row into the outer array. #grid counts the rows and #grid[1] the columns of the first row:

local table10: {{number}} = {}
for i = 1, 3 do
    local row: {number} = {}
    for j = 1, 4 do
        table.insert(row, i * j)
    end
    table.insert(table10, row)
end

Challenge

Easy

Create a 2D typed array gameGrid: {{number}} as a 3×3 grid:

first row 1, 2, 3
second row 4, 5, 6
third row 7, 8, 9

Print the element at the second row, first column, then the element at the third row, third column.

Next, build products: {{number}} with nested loops: for each row i from 1 to 2, create an empty typed row, insert i * j for j from 1 to 3, and insert the row into products.

Finally print the element at row 2, column 3 of products, then the number of rows in products. Four lines of output in total.

Try it yourself

-- Write code here
-- 1) declare gameGrid: {{number}} as the 3x3 grid of 1..9
-- 2) print gameGrid[2][1] and gameGrid[3][3]
-- 3) build products: {{number}} with nested loops (i * j)
-- 4) print products[2][3] and #products