Ruby Recipes: A Problem-Solution Approach

 Contents at a Glance....5 Contents....6 About the Author....19 Acknowledgments....20 Introduction....21 Chapter 1: A Taste of Ruby....25 Small Task, Big Impact....25 Development Environment Installation....26 Windows....26 Mac....26 1.1 The First Recipe: aka Hello World....27 Problem....28 Solution....28 How It Works....28 1.2 Does It Cost Anything to Say Hello?....29 Problem....29 Solution....29 How It Works....30 1.3 Sherlock Holmes and Learning....30 Problem....31 Solution....31 How It Works....31 1.4 1 2 3 4, 1 2 3 4....32 Problem....32 Solution....32 How It Works....33 Interactive Ruby Shell....34 Summary....35 Exercises....35 Exercise 1.1....35 Exercise 1.2....36 Exercise 1.3....36 Chapter 2: Working with Files and Strings....37 Manipulating Strings....37 length or size....37 empty?....37 strip....38 Outline Placeholder....38 Outline Placeholder....38 capitalize....38 downcase and upcase....38 chars....39 index....39 insert....39 delete....39 include?....40 slice....40 count....40 partition....40 tr....40 reverse....41 sub (and gsub)....41 scan....41 split....42 String Formatting....43 2.1 Accepting Input from the Console....43 Problem....43 Solution....43 How It Works....44 2.2 Accepting Numbers as Input....45 Problem....45 Solution....45 How It Works....45 2.3 Handling the Newline....46 Problem....46 Solution....46 More on Getting Rid of the Newline....47 2.4 Formatting Strings....49 Problem....49 Solution....50 How It Works....50 2.5 Processing Command-Line Arguments....51 Problem....51 Solution....51 How It Works....51 2.6 Reading from a File....52 Problem....52 Solution....52 How It Works....53 2.7 Writing to a File....53 Problem....53 Solution....53 How It Works....54 2.8 Getting Started with Exception Handling....54 Problem....54 Solution....55 Initial Execution Context....55 2.9 Importing Code....56 Problem....56 Solution....57 2.10 Creating and Deleting Directories....57 Problem....57 Solution....57 How It Works....58 2.11 Creating a Whole Directory Path....58 Problem....58 Solution....58 How It Works....58 2.12 Reading Multiple Lines from a File....59 Problem....59 Solution....60 How It Works....60 2.13 Reading a File in One Shot....62 Problem....62 Solution....63 How It Works....63 2.14 Working with Strings....63 Problem....63 Solution....63 How It Works....64 Concatenation....65 Expression Evaluation....65 2.15 Converting Numbers to a String....65 Problem....65 Solution....65 2.16 Extracting Information from Strings....66 Problem....66 Task: Change the Order of Names....66 Solution....67 How It Works....67 Task: Totaling the Shopping List....67 Solution....67 Exercises....68 Exercise 2.1....68 Exercise 2.2....68 Chapter 3: Language Elements....69 Commenting on Commenting....69 Variables, Operators …....69 Working with Numbers....70 Logical and Other Operators....72 Reference and Value Equality....72 Checking If an Object Is nil....72 General Comparison Operator....73 Assignment Operators....73 Mass Assignment....74 Bitwise, Logical, and Ternary Operators....74 The Range Operators....75 The dot (.) Operator....75 Some Other Operators....76 Pattern Matching Operators....76 Using Ranges....76 Interval....77 Sequences....77 Conditions....78 Conditional Constructs/Control Flow....79 if....79 nil check....81 unless....82 Ternary operator....82 case....82 while....84 break, redo, next....85 until....86 for....87 3.1 Handling Exceptions....87 Problem....87 Solution....87 Single Line Rescue....88 catch and throw....89 3.2 Working with Predefined Variables and Constants....89 Problem....89 Solution....90 Predefined Constants....92 3.3 Running OS Commands....92 Problem....92 Solution....92 3.4 Initializing and Finalizing Code....92 Problem....92 Solution....93 3.5 Defining Functions....93 Problem....93 Solution....93 Functions with Arguments....94 Function Arguments with Default Values....94 Functions with a Variable Number of Arguments....95 Return Value from Functions....95 Recurrence....96 Exercises....96 Exercise 3.1....96 Exercise 3.2....97 Exercise 3.3....97 Chapter 4: Collections....98 4.1 Creating and Initializing Arrays....99 Problem....99 Solution....99 4.2 Accessing Array Elements....101 Problem....101 Solution....101 4.3 Inserting an Element at a Certain Position....102 Problem....102 Solution....102 4.4 Working with Multidimensional Arrays....103 Problem....103 Solution....103 4.5 Working with Arrays....104 Problem....104 Solution....104 empty?....104 fill....104 Add, Subtract, Compare, and Contrast....105 Outline Placeholder....105 concat....105 Outline Placeholder....105 Outline Placeholder....105 Outline Placeholder....105 Outline Placeholder....106 Outline Placeholder....106 Set Operations....106 | (or union)....106 & (or intersection)....106 uniq....107 In Place Operations....107 sort (and sort!)....107 reverse (and reverse!)....108 Further Access and Manipulation....108 include?....108 index....108 rindex....108 values_at....109 fetch....109 insert....109 delete....110 delete_at....110 join....111 compact....111 clear....111 4.6 Creating Hashes....111 Problem....111 Solution....111 4.7 Adding New Elements to a Hash....112 Problem....112 Solution....112 4.8 Working with Hashes....113 Problem....113 Solution....114 clear....114 empty?....114 has_key?....114 has_value?....114 key....115 fetch....115 values_at....115 delete....116 invert....116 to_a....116 Outline Placeholder....116 merge (and merge!)....117 4.9 Creating a Collection of Unique Objects....117 Problem....117 Solution....117 4.10 Inspecting a Set....118 Problem....118 Solution....118 4.11 Working with Sets....119 Problem....119 Solution....119 Checking and Changing....119 length (or size)....119 empty?....119 include?....119 clear....120 << (or add)....120 merge....120 delete....120 subtract....120 Outline Placeholder....121 Set Operations....121 + (or | or union)....121 & (or intersection)....121 intersect?....122 disjoint?....122 - (or difference)....122 Outline Placeholder....122 Subset and superset....122 Flattening and Conversion....123 Exercises....124 Exercise 4.1....124 Exercise 4.2....124 Chapter 5: Blocks and Iterators....125 5.1 Associating Blocks with Functions....126 Problem....126 Solution....126 5.2 Adding Arguments to a Block....128 Problem....128 Solution....128 5.3 Initializing and Finalizing Code....130 Problem....130 Solution....130 5.4 Iterating over Data....131 Problem....131 Solution....131 each....131 step....134 select and reject....134 For Arrays....135 For Hashes....135 For Sets....136 map or collect....136 For Arrays....137 For Sets....137 For Hashes....137 delete_if and keep_if....138 For Arrays....138 For Sets....138 For Hashes....138 sort....139 Exercises....139 Exercise 5.1....139 Exercise 5.2....140 Exercise 5.3....140 Chapter 6: Input-Output....141 6.1 Querying a CSV File....141 Problem....141 Solution....142 Subtask 1: A Person’s Birthday....142 Writing the Code....142 Testing....144 Subtask 2: ( The Names of) the Youngest and the Oldest Persons....146 Date Handling by API....149 Subtask 3: Persons with a Birthday in a Given Month....150 6.2 Sorting Text....151 Problem....151 Solution....152 How It Works....153 6.3 Checking User Input....153 Problem....153 Solution....153 6.4 Storing Data in a Structured Manner....158 Problem....158 Solution....158 6.5 Working with Directories....160 Problem....160 Solution....160 mkdir....161 rmdir....161 pwd....161 chdir....162 home....162 exist?....162 entries....163 new....163 each....163 foreach....164 glob....164 6.6 Dividing Files into Subdirectories....166 Problem....166 Solution....166 6.7 Adding Text to Files Using a Batch Operation....168 Problem....168 Solution....168 Approach 1: Output From Command Execution....169 Approach 2: Use Dir.glob....170 Adding the Comments in Each File....170 Chapter 7: Regular Expressions....172 7.1 Searching Within a File....172 Problem....172 Solution....174 How It Works....174 7.2 Finding Only the Matched String....176 Problem....176 Solution....176 How It Works....176 7.3 Working with Character Classes....178 Problem....178 Solution....178 How It Works....178 Negation....179 Range....180 Union....180 Intersection....181 Intersection with Negation....181 Common Character Classes....182 Predefined Character Classes....182 Any Single Character: dot....183 Whitespace and Non-Whitespace....183 Special Characters....184 Escape Sequence....185 7.4 Finding Significant Positions in a String....185 Problem....185 Solution....185 End of a Source String....186 Word Boundary and Non-Word Boundary....187 Start and End of a String....188 Interaction of Subpatterns....189 Looking for Multiple Groups....191 7.5 Using Non-Capturing Groups....192 Problem....192 Solution....192 7.6 Understanding the Regex Engine and Backtracking....193 Problem....193 Solution....193 Plane Forward Search....194 Backtracking....194 More on Greedy (Meta-) Characters....195 7.7 Finding Repeated Patterns....196 Problem....196 Solution....196 How It Works....197 Octal Codes and Backreferences....198 Named Backreferences....199 7.8 Finding a Match and Excluding Some of It in the Result....199 Problem....199 Solution....200 Negative Lookahead Assertion....201 Lookbehind Assertion....201 Negative Lookbehind Assertion....202 7.9 Inserting Comments in a Regular Expression....202 Problem....202 Solution....202 7.10 Modifying Results....203 Problem....203 Solution....203 How It Works....204 7.11 Using Non-Backtracking Groups....205 Problem....205 Solution....205 How It Works....205 7.12 Replacing Substrings Using Regular Expressions....206 Problem....206 Solution....206 7.13 Using the scan Function with Regular Expressions....207 Exercises....208 Exercise 7.1....208 Exercise 7.2....209 Chapter 8: Putting It into Action....210 8.1 Removing Block CommentedCode....210 Problem....210 Solution....210 8.2 Searching and Replacing in Text Files....216 Problem....216 Solution....216 8.3 Removing Duplicates from a Text File....221 Problem....221 Solution....221 The Technical Problem Specification....223 Step 1: Remove the Comments....223 Step 2: Remove Optional Keywords....224 Step 3: Collect Tokens....227 Step 4: Get Distinct Values....231 8.4 Reading XML as Text....232 Problem....232 Solution....232 8.5 A Case for Hash Buckets....234 Problem....234 Solution....235 How It Works....236 Appendix A: Solutions to Exercises....237 Solutions for Chapter 1....237 (Solution) Excercise 1.1....237 (Solution) Excercise 1.2....237 (Solution) Excercise 1.3....237 Solutions for Chapter 2....238 (Solution) Excercise 2.1....238 (Solution) Excercise 2.2....238 Solutions for Chapter 3....238 (Solution) Excercise 3.1....238 (Solution) Excercise 3.2....239 (Solution) Excercise 3.3....239 Solutions for Chapter 4....239 (Solution) Excercise 4.1....239 (Solution) Excercise 4.2....240 Solutions for Chapter 5....241 (Solution) Excercise 5.1....241 (Solution) Excercise 5.2....241 (Solution) Excercise 5.3....241 Solutions for Chapter 7....242 (Solution) Excercise 7.1....242 (Solution) Excercise 7.2....242 Index....243