Swift Nested Arrays

A nested array is an array whose values are themselves arrays. Rows of a grid fit this shape well, with one inner array per row.

A grid stored as arrays inside an array

The outer brackets hold two inner arrays. Printing the whole grid shows both rows in one line.

let grid = [[1, 2, 3], [4, 5, 6]]
print(grid)
print(grid.count)
print(grid[0].count)

Reading one cell with two indexes

The two reads here pick the first value of the first row and the last value of the second row. Each read prints a single number.

let grid = [[1, 2, 3], [4, 5, 6]]
print(grid[0][0])
print(grid[1][2])

Printing a grid row by row

Printing the row on each pass shows its values as a list on one line. Three passes give three lines for the three rows.

let grid = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for row in grid {
    print(row)
}

Adding up each row with nested loops

The outer loop takes one row at a time. The inner loop adds every value in that row to a row total.

let grid = [[1, 2, 3], [10, 20]]
for row in grid {
    var total = 0
    for value in row {
        total += value
    }
    print(total)
}

Example

let grid = [[2, 4], [6, 8], [10, 12]]
print(grid[2][1])
var total = 0
for value in grid[1] {
    total += value
}
print(total)
print(grid.count)

Key points

Each inner array is one value inside the outer array.
Write a nested array with an array literal inside another array literal.
Use .count on the outer array to count its inner arrays.
Use .count on one inner array to count the values in that row.
Two indexes written one after the other pick a single value, the row index first.

In this example, the first line stores a grid with three rows of two numbers. The second line prints the value at row 2, column 1, which is 12. The loop then adds the values of row 1, 6 and 8, into total. The next line prints total as 14, and the last line prints the count of rows as 3.

Note

Every inner array in a grid can hold a different number of values.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz Swift Compiler

let grid = [[2, 4], [6, 8], [10, 12]]
print(grid[2][1])
var total = 0
for value in grid[1] {
    total += value
}
print(total)
print(grid.count)

Exercise

A grid holds [[1, 2], [3, 4]]. What does grid[1][0] give?

3 1 2 4