🧵 R Strings & Patterns: Weaving Words Like Magic!

Imagine you’re a word wizard with a magical loom. Every string is a colorful thread, and R gives you the tools to cut, stretch, twist, and weave these threads into beautiful patterns!

🎯 What You’ll Master

Think of strings as friendship bracelets made of letters. Today, you’ll learn to:

• Tie strings together (concatenation)
• Measure and snip them (length & extraction)
• Dress them up nice (formatting)
• Change their voice (case conversion)
• Cut and swap pieces (splitting & replacement)
• Find hidden patterns (pattern matching)
• Create search spells (regular expressions)

1. 🔗 String Concatenation: Tying Strings Together

What Is It?

Concatenation means gluing words together — like linking train cars!

The Magic Spells

paste() — The Friendly Glue

# Joins with a space by default
paste("Hello", "World")
# Result: "Hello World"

# Use sep to change the glue
paste("2024", "12", "25", sep = "-")
# Result: "2024-12-25"

paste0() — The Super Glue (No Gaps!)

paste0("Super", "Hero")
# Result: "SuperHero"

paste0("R", "ocks!")
# Result: "Rocks!"

cat() — The Printer

cat("I", "love", "R!", "\n")
# Prints: I love R!

🎨 Real-Life Example

name <- "Luna"
age <- 8
paste(name, "is", age, "years old!")
# "Luna is 8 years old!"

2. 📏 String Length and Extraction: Measuring & Snipping

Finding Length with nchar()

How many letters are in your word?

nchar("butterfly")
# Result: 9

nchar("R")
# Result: 1

Extracting Pieces with substr()

Cut out a piece like cutting a ribbon!

# substr(text, start, stop)
substr("RAINBOW", 1, 3)
# Result: "RAI"

substr("RAINBOW", 5, 7)
# Result: "BOW"

🎨 Real-Life Example

phone <- "555-123-4567"
area_code <- substr(phone, 1, 3)
# area_code = "555"

3. ✨ String Formatting: Dressing Up Your Words

sprintf() — The Fashion Designer

Make your strings look fancy with placeholders!

sprintf("I have %d apples", 5)
# "I have 5 apples"

sprintf("Pi is %.2f", 3.14159)
# "Pi is 3.14"

sprintf("%s scored %d points!", "Max", 100)
# "Max scored 100 points!"

format() — The Organizer

format(12345.6, big.mark = ",")
# "12,345.6"

format(7, width = 3, justify = "right")
# "  7"

4. 🔄 String Case Conversion: Changing the Voice

The Volume Controls

Think of these as whisper and SHOUT buttons!

# SHOUT! (all uppercase)
toupper("hello world")
# "HELLO WORLD"

# whisper (all lowercase)
tolower("HELLO WORLD")
# "hello world"

Using tools::toTitleCase()

Perfect for Book Titles

tools::toTitleCase("the little prince")
# "The Little Prince"

🎨 Real-Life Example

user_input <- "JoHn SmItH"
clean_name <- tools::toTitleCase(
  tolower(user_input)
)
# "John Smith"

5. ✂️ String Splitting & Replacement: Cut and Swap

strsplit() — The Scissors

Chop a string into pieces!

strsplit("apple,banana,cherry", ",")
# Returns list: "apple" "banana" "cherry"

strsplit("Hello World", " ")
# Returns list: "Hello" "World"

gsub() — Find and Replace All

Swap every match!

gsub("cat", "dog", "I love my cat cat")
# "I love my dog dog"

sub() — Replace First Match Only

sub("cat", "dog", "cat cat cat")
# "dog cat cat"

🎨 Real-Life Example

messy <- "hello...world...R"
clean <- gsub("\\.\\.\\.", " ", messy)
# "hello world R"

6. 🔍 Pattern Matching Functions: The Detective Tools

grep() — Find Which Items Match

Returns positions of matches

fruits <- c("apple", "banana", "apricot", "cherry")
grep("ap", fruits)
# Result: 1 3 (positions of apple, apricot)

grepl() — True or False Detective

Returns TRUE/FALSE for each item

grepl("ap", fruits)
# TRUE FALSE TRUE FALSE

regexpr() — Where’s the Match?

Tells you exactly where the pattern starts

regexpr("an", "banana")
# Returns 2 (match starts at position 2)

🔎 Comparison Chart

graph TD
    A[Pattern Matching] --> B[grep]
    A --> C[grepl]
    A --> D[regexpr]
    B --> E[Returns: Positions]
    C --> F[Returns: TRUE/FALSE]
    D --> G[Returns: Match Location]

7. 🧙‍♂️ Regular Expression Basics: The Magic Spells

What Are Regular Expressions?

Regex = Super-powered search patterns!

Think of them as search wildcards on steroids.

The Essential Magic Symbols

Examples in Action

# Find strings starting with "A"
grep("^A", c("Apple", "Banana", "Avocado"))
# Result: 1 3

# Find strings ending with numbers
grepl("[0-9]quot;, c("Room101", "Kitchen", "Floor2"))
# TRUE FALSE TRUE

# Match email-like patterns
email <- "test@email.com"
grepl("\\w+@\\w+\\.\\w+", email)
# TRUE

🎨 Real-Life Example

# Extract all phone numbers
texts <- c("Call 555-1234", "No number", "Dial 123-5678")
grep("\\d{3}-\\d{4}", texts)
# Result: 1 3

🗺️ The Complete String Journey

graph TD
    A[Raw String] --> B[Concatenate]
    B --> C[Format/Style]
    C --> D[Change Case]
    D --> E[Split if Needed]
    E --> F[Search Patterns]
    F --> G[Replace/Extract]
    G --> H[Clean Result!]

🎁 Quick Reference Summary

🚀 You Did It!

You’ve just learned to:

• ✅ Glue strings together with paste() and paste0()
• ✅ Measure and cut with nchar() and substr()
• ✅ Format beautifully with sprintf()
• ✅ Change case with toupper() and tolower()
• ✅ Split and replace with strsplit(), gsub(), sub()
• ✅ Hunt patterns with grep(), grepl(), regexpr()
• ✅ Cast regex spells with special symbols!

You’re now a String Wizard! 🧙‍♂️✨