{"id":2665,"date":"2026-02-05T09:39:45","date_gmt":"2026-02-05T09:39:45","guid":{"rendered":"https:\/\/demo.materiamedica.net\/demo6\/?p=2665"},"modified":"2026-02-05T09:39:45","modified_gmt":"2026-02-05T09:39:45","slug":"chapter-40-swift-arrays-multidimensional","status":"publish","type":"post","link":"https:\/\/demo.materiamedica.net\/demo6\/chapter-40-swift-arrays-multidimensional\/","title":{"rendered":"Chapter 40: Swift Arrays: Multidimensional"},"content":{"rendered":"1. What is a Multidimensional Array?<\/h3>\n
A multidimensional array<\/strong> is simply an array of arrays<\/strong>.<\/p>\nIn other words:<\/p>\n
\n- You have an outer array<\/li>\n
- Each element of the outer array is itself an array<\/strong><\/li>\n
- So you access elements using two (or more) indices<\/strong><\/li>\n<\/ul>\n
Real-life analogies:<\/p>\n
\n- 2D array<\/strong> \u2192 chessboard (8 rows \u00d7 8 columns)<\/li>\n
- 2D array<\/strong> \u2192 monthly calendar (weeks as rows, days as columns)<\/li>\n
- 2D array<\/strong> \u2192 spreadsheet table (rows and columns)<\/li>\n
- 3D array<\/strong> \u2192 stack of chessboards, or RGB image (height \u00d7 width \u00d7 color channels)<\/li>\n<\/ul>\n
In Swift we usually talk about 2D arrays<\/strong> (most common), sometimes 3D<\/strong>, and rarely more.<\/p>\n2. Creating a 2D Array \u2014 all common ways<\/h3>\nWay 1 \u2013 Literal syntax (most readable for small fixed data)<\/h4>\n\n
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Swift<\/div>\n
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let matrix = [\r\n [1, 2, 3],\r\n [4, 5, 6],\r\n [7, 8, 9]\r\n]\r\n\r\n\/\/ Access: row 1 (second row), column 2 (third number)\r\nprint(matrix[1][2]) \/\/ 6<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nWay 2 \u2013 Empty 2D array with fixed rows & columns<\/h4>\n\n
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Swift<\/div>\n
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let rows = 4\r\nlet columns = 5\r\n\r\nvar grid = Array(repeating: Array(repeating: 0, count: columns), count: rows)\r\n\r\n\/\/ Now grid is:\r\n\/\/ [ [0,0,0,0,0],\r\n\/\/ [0,0,0,0,0],\r\n\/\/ [0,0,0,0,0],\r\n\/\/ [0,0,0,0,0] ]<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nWay 3 \u2013 From existing data (very common)<\/h4>\n\n
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Swift<\/div>\n
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let sales2024 = [\r\n [\"Jan\", \"Feb\", \"Mar\", \"Apr\"],\r\n [12000, 15000, 18000, 14000],\r\n [13000, 16000, 19000, 14500]\r\n]<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n3. Reading from a 2D Array<\/h3>\n\n
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Swift<\/div>\n
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let chessBoard = [\r\n [\"\u265c\", \"\u265e\", \"\u265d\", \"\u265b\", \"\u265a\", \"\u265d\", \"\u265e\", \"\u265c\"],\r\n [\"\u265f\", \"\u265f\", \"\u265f\", \"\u265f\", \"\u265f\", \"\u265f\", \"\u265f\", \"\u265f\"],\r\n [\" \", \" \", \" \", \" \", \" \", \" \", \" \", \" \"],\r\n [\" \", \" \", \" \", \" \", \" \", \" \", \" \", \" \"],\r\n [\" \", \" \", \" \", \" \", \" \", \" \", \" \", \" \"],\r\n [\" \", \" \", \" \", \" \", \" \", \" \", \" \", \" \"],\r\n [\"\u2659\", \"\u2659\", \"\u2659\", \"\u2659\", \"\u2659\", \"\u2659\", \"\u2659\", \"\u2659\"],\r\n [\"\u2656\", \"\u2658\", \"\u2657\", \"\u2655\", \"\u2654\", \"\u2657\", \"\u2658\", \"\u2656\"]\r\n]\r\n\r\n\/\/ Piece at row 0, column 4 (black king)\r\nprint(chessBoard[0][4]) \/\/ \u265a\r\n\r\n\/\/ White pawn at row 6, column 3\r\nprint(chessBoard[6][3]) \/\/ \u2659<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nSafe access (very important)<\/strong><\/p>\n\n
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Swift<\/div>\n
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func safeGet<T>(array: [[T]], row: Int, col: Int) -> T? {\r\n guard row >= 0, row < array.count,\r\n col >= 0, col < array[row].count else {\r\n return nil\r\n }\r\n return array[row][col]\r\n}\r\n\r\nprint(safeGet(array: chessBoard, row: 0, col: 4) ?? \"Empty\") \/\/ \u265a\r\nprint(safeGet(array: chessBoard, row: 10, col: 5) ?? \"Empty\") \/\/ Empty<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n4. Modifying a 2D Array (only if var)<\/h3>\n\n
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Swift<\/div>\n
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var scores = [\r\n [85, 92, 78],\r\n [88, 95, 90],\r\n [76, 82, 87]\r\n]\r\n\r\n\/\/ Change value\r\nscores[1][2] = 99 \/\/ second row, third column \u2192 90 \u2192 99\r\n\r\n\/\/ Add new row\r\nscores.append([80, 85, 88])\r\n\r\n\/\/ Add new column to every row (careful!)\r\nfor i in 0..<scores.count {\r\n scores[i].append(0) \/\/ add 0 as default\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n5. Looping over 2D Arrays \u2014 most common patterns<\/h3>\nPattern 1 \u2013 Nested for-in (classic & clear)<\/h4>\n\n
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Swift<\/div>\n
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let matrix = [\r\n [1, 2, 3],\r\n [4, 5, 6],\r\n [7, 8, 9]\r\n]\r\n\r\nprint(\"Matrix:\")\r\nfor row in matrix {\r\n for number in row {\r\n print(number, terminator: \" \")\r\n }\r\n print() \/\/ new line after each row\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nOutput:<\/strong><\/p>\n\n
\n
\n
text<\/div>\n
\n
1 2 3 \r\n4 5 6 \r\n7 8 9<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nPattern 2 \u2013 With row & column indices<\/h4>\n\n
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Swift<\/div>\n
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for (rowIndex, row) in matrix.enumerated() {\r\n for (colIndex, value) in row.enumerated() {\r\n print(\"Position [\\(rowIndex),\\(colIndex)] = \\(value)\")\r\n }\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nPattern 3 \u2013 Using indices<\/h4>\n\n
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Swift<\/div>\n
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for rowIndex in matrix.indices {\r\n for colIndex in matrix[rowIndex].indices {\r\n print(matrix[rowIndex][colIndex], terminator: \" \")\r\n }\r\n print()\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n6. Real-Life Examples You Will Actually Write<\/h3>\nExample 1 \u2013 Monthly sales table<\/h4>\n\n
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Swift<\/div>\n
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let months = [\"Jan\", \"Feb\", \"Mar\", \"Apr\"]\r\nlet products = [\"Phone\", \"Laptop\", \"Tablet\"]\r\n\r\nlet sales: [[Int]] = [\r\n [120, 150, 180], \/\/ Phone sales per month\r\n [45, 60, 55], \/\/ Laptop\r\n [80, 95, 110] \/\/ Tablet\r\n]\r\n\r\nprint(\"Monthly Sales (\u20b9000s)\")\r\nprint(\" \" + months.joined(separator: \" \"))\r\n\r\nfor (productIndex, productSales) in sales.enumerated() {\r\n let row = \"\\(products[productIndex]) \" + productSales.map { String(format: \"%4d\", $0) }.joined(separator: \" \")\r\n print(row)\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nExample 2 \u2013 Tic-tac-toe board<\/h4>\n\n
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Swift<\/div>\n
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var board = [\r\n [\" \", \" \", \" \"],\r\n [\" \", \" \", \" \"],\r\n [\" \", \" \", \" \"]\r\n]\r\n\r\n\/\/ Place X in center\r\nboard[1][1] = \"X\"\r\n\r\n\/\/ Place O in corner\r\nboard[0][0] = \"O\"\r\n\r\n\/\/ Print board\r\nfor row in board {\r\n print(row.joined(separator: \" | \"))\r\n print(\"---------\")\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n7. Very Common Beginner Mistakes & Correct Habits<\/h3>\n\n
\n
\n\n\n| Mistake<\/th>\n | Wrong \/ Dangerous code<\/th>\n | Correct \/ Safe habit<\/th>\n | Why?<\/th>\n<\/tr>\n<\/thead>\n |
\n\n| Forgetting outer array can be empty<\/td>\n | matrix[0][0] without check<\/td>\n | guard !matrix.isEmpty else { \u2026 }<\/td>\n | Crash if no rows<\/td>\n<\/tr>\n |
\n| Assuming all rows have same length<\/td>\n | matrix[row][col] without check<\/td>\n | if col < matrix[row].count { \u2026 }<\/td>\n | Rows can have different lengths<\/td>\n<\/tr>\n |
\n| Force-unwrapping first\/last of inner array<\/td>\n | matrix[0].first!<\/td>\n | matrix[0].first ?? default<\/td>\n | Inner array can be empty<\/td>\n<\/tr>\n |
\n| Modifying let array<\/td>\n | let grid = \u2026; grid[0][0] = 99<\/td>\n | Use var if you need to change<\/td>\n | Immutable<\/td>\n<\/tr>\n |
\n| Using fixed indices without validation<\/td>\n | matrix[5][5]<\/td>\n | Use indices.contains or safe subscript<\/td>\n | Out-of-bounds \u2192 crash<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n 8. Quick Reference \u2013 Most Useful 2D Array Operations<\/h3>\n\n \n \n\n\n| Goal<\/th>\n | Recommended code<\/th>\n | Notes<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Create empty 2D grid<\/td>\n | Array(repeating: Array(repeating: 0, count: cols), count: rows)<\/td>\n | Classic way<\/td>\n<\/tr>\n | \n| Safe element access<\/td>\n | matrix[safe: row]?[safe: col] ?? default<\/td>\n | With safe subscript extension<\/td>\n<\/tr>\n | \n| Loop with row & column indices<\/td>\n | for r in matrix.indices { for c in matrix[r].indices { \u2026 } }<\/td>\n | Most explicit & safe<\/td>\n<\/tr>\n | \n| Print nicely<\/td>\n | matrix.map { $0.map(String.init).joined(separator: ” “) }.joined(separator: “\\n”)<\/td>\n | Quick debug print<\/td>\n<\/tr>\n | \n| Get row<\/td>\n | matrix[2]<\/td>\n | Returns Array (copy)<\/td>\n<\/tr>\n | \n| Get column (trickier)<\/td>\n | (0..<matrix.count).map { matrix[$0][col] }<\/td>\n | No built-in column access<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n 9. Small Practice \u2013 Try these<\/h3>\n\n- Create a 4\u00d75 grid filled with zeros \u2192 Set position [1][2] = 99 \u2192 Print the grid row by row<\/li>\n
- Create a 3\u00d73 tic-tac-toe board \u2192 Place “X” in center \u2192 Place “O” in all four corners \u2192 Print the board with nice separators<\/li>\n
- Create a sales table (3 products \u00d7 4 months) \u2192 Print it like a real table with headers<\/li>\n<\/ol>\n
Paste your code here if you want feedback or cleaner versions!<\/p>\n What would you like to explore next about arrays?<\/p>\n \n- Sorting<\/strong> 2D arrays (by row, by column, custom)<\/li>\n
- Transposing<\/strong> a matrix (rows \u2194 columns)<\/li>\n
- Flattening<\/strong> 2D \u2192 1D and vice versa<\/li>\n
- Multidimensional arrays in SwiftUI<\/strong> (grids, tables)<\/li>\n
- Arrays vs ArraySlice<\/strong> vs ContiguousArray<\/strong><\/li>\n
- Or move to another topic (dictionaries, sets, optionals\u2026)<\/li>\n<\/ul>\n
Just tell me \u2014 we\u2019ll keep going in the same clear, detailed, patient style \ud83d\ude0a<\/p>\n","protected":false},"excerpt":{"rendered":" 1. What is a Multidimensional Array? A multidimensional array is simply an array of arrays. In other words: You have an outer array Each element of the outer array is itself an array So...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[76],"tags":[],"class_list":["post-2665","post","type-post","status-publish","format-standard","hentry","category-swift"],"_links":{"self":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2665","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/comments?post=2665"}],"version-history":[{"count":1,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2665\/revisions"}],"predecessor-version":[{"id":2666,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2665\/revisions\/2666"}],"wp:attachment":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/media?parent=2665"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/categories?post=2665"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/tags?post=2665"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}} | |